CN102923997B - Method for preparing high-strength semi-regenerative coarse aggregate concretes - Google Patents

Abstract

The invention discloses a method for preparing high-strength semi-regenerated coarse aggregate concrete, which belongs to the technical field of recycled coarse aggregate concrete. The preparation method refers to the amount of glue used in ordinary concrete, and by adjusting the amount of admixtures, mineral powder and fly ash, a high-performance semi-recycled coarse aggregate concrete with good workability, high early strength and good later strength development can be prepared.

Description

Preparation method of high-strength semi-recycled coarse aggregate concrete

technical field

The invention relates to a method for preparing high-strength semi-regenerated coarse aggregate concrete, in particular to a method for preparing semi-regenerated high-strength concrete above 50Mpa by using a composite double-mixing technology of adding primary fly ash and slag under the condition of a high-efficiency water reducer. Technical field of recycled coarse aggregate concrete.

technical background

Semi-recycled coarse aggregate concrete is a kind of recycled concrete prepared by replacing 30%-50% of the natural aggregate in ordinary concrete with recycled coarse aggregate. The concrete removed from the building is manually classified, crushed, cleaned, and graded to form continuously graded recycled aggregates instead of natural aggregates, which not only handles a large amount of construction waste, but also reduces its environmental pollution and waste of land resources. Moreover, the actual project of reusing the garbage saves the amount of natural sand and gravel. Therefore, recycled concrete is a green building product that can be recycled efficiently. The research and application of recycled concrete has attracted more and more attention from scholars at home and abroad.

However, due to the characteristics of recycled aggregates which are different from natural aggregates, such as the cracks generated during the crushing process of recycled aggregates, the crushing index of recycled aggregates is low; the surface of recycled aggregates is attached to the original old cement slurry, The porosity of the recycled aggregate is higher than that of the natural aggregate; the recycled aggregate contains more impurities such as mud and sand. These characteristics have an adverse effect on the strength of recycled concrete. Under the same proportion, the strength of recycled concrete is generally lower than that of ordinary concrete. At present, the mix ratio design of recycled concrete generally refers to the design method of ordinary concrete. Some scholars propose to adopt the method of compacting the skeleton with embedded extrusion. The present invention uses the absolute volume method to prepare recycled concrete on the basis of referring to the amount of ordinary concrete glue. The strength of recycled concrete prepared by existing domestic scholars is generally below C40, and there are few preparations for high-strength recycled coarse aggregate concrete. At present, American scholars have prepared recycled coarse aggregate concrete above C60 by adding silica fume. In view of the insufficient research on the proportion of high-strength recycled concrete, the present invention adds an appropriate amount of primary fly ash and slag (>=S95) to the mix proportion to prepare a concrete with good work performance, high early strength and fast development of later strength. High-strength semi-recycled coarse aggregate concrete with a compressive strength above 50Mpa.

Contents of the invention

The purpose of the present invention is to solve the problem that the existing semi-regenerated coarse aggregate concrete has low strength and cannot meet the needs of actual engineering. Based on the double-mixing technology of the absolute volume method, the prepared product has good working performance, high early strength, fast development of late strength, and low collapse. Large fluidity and high strength semi-recycled coarse aggregate concrete whose slump meets pumpability requirements. In the present invention, a high-efficiency water reducer (water reducing rate>=25%) is added to the mix ratio, and an appropriate amount of primary fly ash and ultrafine mineral powder (>=S95) are added at the same time. Next, improve the workability of concrete and increase the compressive strength.

The technical solution adopted by the present invention for realizing the above object is as follows.

The preparation method of high-strength semi-recycled coarse aggregate concrete comprises the following steps:

(1) Determine the amount of each substance,

First determine the amount of cement; the amount of primary fly ash refers to ordinary concrete, using the excess coefficient substitution method, the primary fly ash replaces 10%-30% of the cement mass, and the primary fly ash excess coefficient takes 1.1- 1.2; the amount of mineral powder accounts for 10%-25% of the cement mass; the amount of high-efficiency water-reducing agent accounts for 1.8%-3% of the total amount of cementitious materials, and the water-reducing rate of the above-mentioned high-efficiency water-reducing agent is preferably 28%; C65 The water-binder ratio of semi-recycled coarse aggregate concrete is controllable between 0.28-0.33, and the amount of cement per cubic meter is 450kg-500kg; the water-binder ratio of C60 semi-recycled coarse aggregate concrete is between 0.34-0.39, and the amount of cement per cubic meter 350kg-400kg; the water-binder ratio of C55 semi-recycled coarse aggregate concrete is between 0.40-0.45, and the amount of concrete cement per cubic meter is 300kg-350kg; the sand rate adopts the sand rate of ordinary concrete (can be determined according to actual experience or refer to "Ordinary Concrete According to the value of sand rate in Design Regulations (JGJ55-2011), if there is no historical experience, the sand rate will be calculated according to the formula 1-1 according to the gap of coarse aggregate filled with sand and a little surplus.

${\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

β _s - Sand rate

ρ _s - sand apparent density

ρ _g - apparent density of coarse aggregate

_Pg - Coarse aggregate porosity

α-Putting coefficient, 1.1-1.2 for mechanical vibration, 1.2-1.4 for manual vibration;

$\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; co</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; go</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; go</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; so</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; fo</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; the\; ko</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; the\; w</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1000</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}$

${\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; so</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; so</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; go</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; go</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}$

m _co , m _go1 , m _go2 , m _so , m _fo , m _ko , m _wo - mass of cement, coarse aggregate, recycled coarse aggregate, sand, fly ash, mineral powder, water per cubic meter of concrete, respectively ,

ρ _c , ρ _g1 , ρ _g2 , ρ _s , ρ _f , ρ _k , ρ _w - respectively the density of cement, coarse aggregate, recycled coarse aggregate, sand, fly ash, mineral powder, water,

a- volume percentage of air content in concrete, no air-entraining agent a=1,

β _s - sand rate;

The technical index requirements of the above-mentioned primary fly ash are shown in Table 1-1

Fineness Water demand ratio Loss on ignition Moisture content Sulfur trioxide content <=12% <=95 <=5% <=11% <=3%

(2) According to the theoretical dosage of each material determined in step (1), then calculate the actual dosage ratio of each material according to the measured moisture content of sand and coarse aggregate.

(3) Wet the inner surface of the mixer first, then add the regenerated coarse aggregate into the mixer, turn on the mixer and add part of the water evenly into the mixer and stir for 2-3 minutes.

(4) After the regenerated coarse aggregate absorbs water, add coarse aggregate, sand, fly ash, mineral powder, and cement into the mixer, turn on the mixer, add high-efficiency water reducer to the water and mix evenly, and then slowly add water to the mixer Stir.

According to the actual situation, if the fluidity does not meet the requirements of use after stirring for 5-10 minutes in step (4), the following steps can also be included: (5) Add 0.1%-0.2% of the total mass of fly ash, mineral powder, and cement Stir with high-efficiency water reducer; if the requirements are not met after adding high-efficiency water reducer, add 1%-3% of the total mass of fly ash, mineral powder, and cement to adjust its fluidity. The mixture of semi-regenerated coarse aggregate concrete was left to stand for about 20 minutes, and the loss of slump was observed. If the slump meets the requirements for use, vibrate the mixture into shape. On the basis of the above step (5), if the slump does not meet the requirements for use, repeat step (5) again.

The recycled aggregate is preferably recycled aggregate that is continuously graded within the range of 5-25mm,

Compared with the existing method for preparing semi-regenerated coarse aggregate concrete, the present invention has the following characteristics

1 Under the condition of high-efficiency reducer, the composite double-admixture technology of adding primary fly ash and slag powder (>=S95) is adopted. Adding a high-efficiency reducer effectively reduces the water-binder ratio, which is a necessary condition for obtaining high-strength concrete; adding first-grade fly ash to improve the workability of concrete; adding mineral powder (>=S95) to stimulate cement activity and improve concrete strength. Under the condition of low water-binder ratio, the concrete with large flow is obtained, which overcomes the disadvantage of low strength of recycled concrete.

2 Under the condition that the total amount of glue material is equivalent to that of ordinary concrete, the strength of recycled concrete is improved, the cost of recycled concrete is reduced, and recycled concrete is more easily applied in projects.

3. There is no particularly strict requirement on recycled aggregate except particle size, and the applicability of the present invention is wider.

Detailed ways

Based on the above method steps, 7 groups of semi-regenerated coarse aggregate concrete were prepared, and the compressive strength of semi-regenerated coarse aggregate concrete at 3d, 7d, and 28d was measured. The 3-day strength reaches 50% of the 28-day strength, and the 7-day strength reaches 70% of the 28-day strength, which meets the project's requirements for the early strength of concrete. The compressive strength of recycled coarse aggregate concrete in 28 days and a half is above 50Mpa, and the highest strength reaches 75.1 Mpa, greatly improving the strength of the existing semi-recycled coarse aggregate concrete.

Example 1

1 selection of materials

It is preferred to select recycled aggregates with continuous gradation in the particle size range of 5-25mm, with water absorption rate of 3.23%, moisture content of 1%, crushing index of 12.51%, apparent density of 2290kg/m3, and porosity of 44.3%. Ordinary aggregates with a particle size of 5-25mm and continuous gradation are preferred, with a moisture content of 1% and an apparent density of 2760kg/m3. Xingda first grade fly ash, density 2300kg/m3. The sand is natural medium sand with a water content of 5%-9%, a stone content of 15%-25%, and an apparent density of 2670kg/m3. Silver water mineral powder (S95) has an apparent density of 1227kg/m3. 42.5 grade Beishui cement has an apparent density of 3100kg/m3. Polycarboxylate high-efficiency water reducer (water reducing rate 28%) has a density of 1130kg/m3 and a solid content of 10%. The water is tap water with a density of 1000kg/m3.

2 mix ratio calculation

(1) Determine the sand rate

According to historical test experience, the actual sand rate is 47%.

(2) Determine the amount of glue material and the ratio of water to glue

The amount of cement per cubic meter is 420kg, the replacement rate of primary fly ash is 15%, the excess coefficient is 1.13, the cement consumption after replacement is 356kg/m3, mineral powder (S95) is added to 13.5% of the cement mass, and the water-cement ratio is 0.37. The dosage of high-efficiency water reducer (28% water reduction rate) is 2.1%.

(3) Calculate the amount of sand, ordinary coarse aggregate and recycled coarse aggregate

Substitute the amount of cementitious material, water amount and high-efficiency water reducer (water reducing rate 28%) obtained in steps (1) and (2) into formula 1-2, 1-3 to calculate sand, natural coarse aggregate and recycled coarse aggregate. Aggregate dosage.

(4) Theoretical mix ratio and actual mix ratio of semi-recycled coarse aggregate concrete

The actual water content of the sand is 6.7%, and the solid content of the high-efficiency water reducer (28% water reduction rate) is 10%. Convert the theoretical mix ratio into actual mix ratio as shown in Table 1-2.

Table 1-2 Mixing ratio of semi-recycled coarse aggregate concrete (unit: kg)

315L semi-recycled concrete trial mixing process

(1) Weigh 15L of each raw material according to Table 1-2.

(2) Wet the inner surface of the mixer first, then add the recycled coarse aggregate into the mixer, turn on the mixer and evenly add a part of the water into the mixer and stir for 2-3 minutes.

(3) After the regenerated coarse aggregate absorbs water for 10 minutes, add ordinary coarse aggregate, sand, and cementitious materials to the mixer in sequence, turn on the mixer, add high-efficiency water reducer (water reducing rate 28%) into the water and mix evenly, and then put Water was slowly added to the mixer and the properties of the mixture were observed. After stirring for 5-10 minutes, observe the fluidity and water retention of the mixture.

(4) If the fluidity is too poor, add 0.1%-0.2% high-efficiency water-reducing agent (water-reducing rate 28%) of the mass of the gelling material and stir, and it is still not satisfied after adding high-efficiency water-reducing agent (water-reducing rate 28%) It is required to add 1%-3% of the total amount of water to adjust its fluidity. The mixture of semi-regenerated coarse aggregate concrete was left to stand for about 20 minutes, and the loss of slump was observed. If the slump meets the requirements for use, vibrate the mixture into shape.

(5) If the slump does not meet the requirements for use, repeat step (4).

Example 2-7

Example 2-7 The preparation of semi-recycled coarse aggregate concrete, the selection of materials and the calculation of the mix ratio are basically the same as in Example 1. According to the calculation in step 2, the mix ratio of each group of semi-recycled concrete 1m ³ is shown in Table 1-3; the trial mixing process is the same Step 3.

Table 1-3 Example 2-7 group semi-recycled coarse aggregate concrete mix ratio

Embodiment 1-7 Measured value of compressive strength of semi-regenerated coarse aggregate concrete

Table 1-4 Example 1-7 Semi-regenerated coarse aggregate concrete 3 days, 7 days and 28 days strength measured values

Mix ratio number 3-day compressive strength/Mpa 7-day compressive strength/Mpa 28 days compressive strength/Mpa Example 1 31.3 40.9 61.7 Example 2 28.3 31.0 53.4 Example 3 32.9 46.0 58.9 Example 4 38.4 46.0 64.1 Example 5 41.7 51.7 68.5 Example 6 50.3 60.0 75.1 Example 7 49.1 57.2 74.4

Claims (6)

1. high more than half regenerated coarse aggregate preparation method of concrete, is characterized in that, comprises the following steps:

(1) determine that first each material consumption determine the consumption of cement; One-level doping quantity of fly ash, with reference to normal concrete, adopts exceeding quantity coefficient method of substitution, and first level flour coal ash replaces cement quality 10%-30%, and first level flour coal ash exceeding quantity coefficient is got 1.1-1.2; Contents of ground slag accounts for cement quality 10%-25%; High efficiency water reducing agent consumption accounts for binder total amount 1.8%-3%, the preferred water reducer water-reducing rate 28% of described high efficiency water reducing agent; C65 half regenerated coarse aggregate water-binder ratio is controlled between 0.28-0.33, every cubic metre of cement consumption 450kg-500kg; C60 half regenerated coarse aggregate water-binder ratio between 0.34-0.39, every cubic meter of concrete cement consumption 350kg-400kg; C55 half regenerated coarse aggregate water-binder ratio between 0.40-0.45, every cubic meter of concrete cement consumption 300kg-350kg; Sand coarse aggregate ratio adopts the sand coarse aggregate ratio of normal concrete or presses sand and fill coarse aggregate space, and slight surplus, calculates by 1-1 formula; Then the 30-50% that accounts for the total mass of regenerated coarse aggregate and aggregate according to 1-2 and 1-3 and regenerated coarse aggregate calculates each material magnitude relation;

${\mathrm{\&beta;}}_s=\mathrm{\&alpha;}\frac{P_g{\mathrm{\&rho;}}_s}{P_g{\mathrm{\&rho;}}_s+{\mathrm{\&rho;}}_g}---1-1$

β _s-sand coarse aggregate ratio

ρ _s-sand apparent density

ρ _g-coarse aggregate apparent density

P _g-coarse aggregate porosity

α-push coefficient aside, adopts machinery to vibrate and gets 1.1-1.2, manually vibrates and gets 1.2-1.4;

$\frac{m_{\mathrm{co}}}{{\mathrm{\&rho;}}_c}+\frac{m_{\mathrm{go}1}}{{\mathrm{\&rho;}}_{g1}}+\frac{m_{\mathrm{go}2}}{{\mathrm{\&rho;}}_{g2}}+\frac{m_{\mathrm{so}}}{{\mathrm{\&rho;}}_s}+\frac{m_{\mathrm{fo}}}{{\mathrm{\&rho;}}_f}+\frac{m_{\mathrm{ko}}}{{\mathrm{\&rho;}}_k}+\frac{m_{\mathrm{wo}}}{{\mathrm{\&rho;}}_w}+10a=1000---1-2$

${\mathrm{\&beta;}}_s=\frac{m_{\mathrm{so}}}{m_{\mathrm{so}}+m_{\mathrm{go}1}+m_{\mathrm{go}2}}---1-3$

M _co, m _go1, m _go2, m _so, m _fo, m _ko, m _wo-be respectively every cubic meter of concrete cement, coarse aggregate, regenerated coarse aggregate, sand, flyash, breeze, the quality of water;

ρ _c, ρ _g1, ρ _g2, ρ _s, ρ _f, ρ _k, ρ _w-be respectively cement, coarse aggregate, regenerated coarse aggregate, sand, flyash, breeze, the density of water;

A-Air Content of Air-entrained Concrete percent by volume, does not add air entrapment agent a=1;

β _s-sand coarse aggregate ratio;

(2), according to the theoretical consumption of the definite each material of step (1), then calculate again the consumption proportion of actual each material according to the water ratio of actual measurement sand and coarse aggregate;

(3) first that stirrer internal surface is wetting, then regenerated coarse aggregate is added in stirrer, open stirrer and a part of water is evenly added and in stirrer, stirs 2-3 minute;

(4) after regenerated coarse aggregate water suction, then common coarse aggregate, sand, flyash, breeze, cement are added in stirrer, open stirrer, high efficiency water reducing agent is added to the water and is mixed, then water is added in stirrer and stirred.

2. according to the method for claim 1, it is characterized in that, according to practical situation, do not meet service requirements in step (4) if stir mobility after 5-10 minute, also comprise the steps: again that the high efficiency water reducing agent of (5) interpolation flyash, breeze, cement total mass 0.1%-0.2% stirs; After adding high efficiency water reducing agent, also do not meet the demands, the water that adds flyash, breeze, cement total mass 1%-3% regulates its mobility.

3. according to the method for claim 2, it is characterized in that, in above-mentioned steps (5) if basis on the slump do not meet service requirements, repeating step (5) again.

4. according to the method for claim 1, it is characterized in that the regeneration aggregate of continuous grading within the scope of the preferred 5-25mm of regeneration aggregate.

5. according to the method for claim 1, it is characterized in that breeze >=S95.

6. according to the method for claim 1, it is characterized in that high efficiency water reducing agent water-reducing rate 28%.