CN112062526B

CN112062526B - Low-strength low-permeability concrete and preparation method thereof

Info

Publication number: CN112062526B
Application number: CN202010942578.4A
Authority: CN
Inventors: 李军心; 黄华; 陈国宝; 曾平; 王金兵; 祝国梁; 蔡玉长生; 王成龙; 陈明法
Original assignee: China Construction Fourth Engineering Division Corp Ltd; China Construction Fourth Engineering Bureau Construction and Development Co Ltd
Current assignee: China Construction Fourth Engineering Division Corp Ltd; China Construction Fourth Engineering Bureau Construction and Development Co Ltd
Priority date: 2020-09-09
Filing date: 2020-09-09
Publication date: 2022-07-12
Anticipated expiration: 2040-09-09
Also published as: CN112062526A

Abstract

The embodiment of the invention provides low-strength low-permeability concrete and a preparation method thereof, wherein concrete mixtures comprise cement, fly ash, clay, sand, water and a water reducing agent; the concrete mixture comprises the following components in percentage by mass: cement: fly ash: clay: sand: water: water reducing agent (82.9-117): (175.6-210.7): (1118-1235.2): (527-643.9): (320-330): (17-18), wherein the total mass of each cubic concrete mixture is 2300-2400 kg. The low-strength low-permeability concrete provided by the invention has good concrete workability, is convenient to construct, has better impermeability and is suitable for underground engineering; and the materials are convenient to obtain, and the economy is good.

Description

Low-strength low-permeability concrete and preparation method thereof

Technical Field

The invention relates to the field of building materials, in particular to a preparation method of low-strength low-permeability concrete.

Background

Concrete is a common and most common building material for construction engineering, the common concrete strength grade of foundation structures in the engineering is C15-C30, the common concrete strength grade of main body structures is C40-C60, the concrete is developed towards higher strength all the time, and even a plurality of concrete with the strength grade of C80-C100 are widely applied to the engineering. The cementitious material of concrete is mainly cement, and generally speaking, the more cement is used, the higher the strength grade of concrete is. The lower the strength grade of the cement, the lower the strength of the concrete when the amount of cement is smaller. But the larger the cement consumption is, the plasticity of the concrete is deteriorated, and the application of the high-efficiency water reducing agent is benefited to improve the construction performance of the high-strength concrete. The higher the strength of the concrete, the higher the compactness of the internal structure of the concrete, the better the impermeability, and the lower the strength of the concrete, the poorer the impermeability of the concrete.

In foundation ditch engineering supporting construction, generally can set up the stagnant water stake in the fender post outside, laminate mutually with the fender post for the outer wall of whole foundation ditch becomes concrete pile wall. The fender piles are used for bearing the pressure of the soil slope, and the water stop piles are arranged between the fender piles and used for stopping underground water seeped from the soil slope between the two fender piles. The stagnant water stake is no steel framework's pure concrete pile, as the name implies, and the biggest effect of stagnant water stake is used for the stagnant water, must have low water permeability. On the other hand, in order to achieve the water stopping effect, the general design adopts secant pile construction, and concrete with lower strength is adopted for the convenience of construction. However, the conventional low-strength concrete has large internal porosity and good water permeability, and is not suitable for the water-stop pile.

It would therefore be of great importance if a concrete could be developed which had low strength and at the same time low water permeability.

Disclosure of Invention

In view of this, the present invention aims to provide a low-strength low-permeability concrete and a preparation method thereof, so as to provide a concrete which is low in cost and can meet the requirements of water-stop piles.

According to the low-strength low-permeability concrete provided by the embodiment of the invention, a concrete mixture comprises cement, fly ash, clay, sand, water and a water reducing agent;

the concrete mixture comprises the following components in percentage by mass: cement: fly ash: clay: sand: water: (ii) a water reducing agent (82.9-117): (175.6-210.7): (1118-1235.2): (527-643.9): (320-330): (17.2-17.6), and the total mass of each cubic concrete mixture is 2300-2400 kg.

Preferably, the clay is a clay with plasticity index > 17.

Preferably, the cement is a slag portland cement having a strength grade of 32.5.

Preferably, the sand is medium sand.

Preferably, the fly ash is class F first grade fly ash.

Preferably, the water reducing agent is a polycarboxylic acid high-performance water reducing agent, and the water reducing rate is not lower than 30%.

The preparation method of the low-strength low-permeability concrete comprises the following steps:

s1: mixing 40-60 liters of concrete in a trial mode, and determining the using amount of each component according to the mass ratio of the components of each cubic concrete mixture;

s2: beating the massive clay into blocks with the particle size smaller than 50mm, taking out 15-20% of water to wet the inner wall of the stirrer, adding the weighed clay and sand into the stirrer, and stirring for 30-40 s; adding cement and fly ash, then adding 50-60% of water, and stirring for 40-60 s; then adding a water reducing agent and the rest water, and stirring for 120-150 s;

s3: taking out part of the mixture and putting the mixture into a slump bucket to measure the slump; if the slump is less than 100mm, increasing the using amount of water in the original proportion, and correspondingly adjusting the using amount of the rest of the mixture; if the slump is larger than 150mm, reducing the using amount of water; if the slump is between 100 and 150mm, taking out the mixture for mold-filling maintenance, maintaining for 28 days under standard maintenance conditions, and measuring the compressive strength of the mold-filling test block;

s4, if the compressive strength is between 10 and 20Mpa, the required concrete is prepared according to the dosage of each component determined in the step S1.

The application of the low-strength low-permeability concrete in manufacturing the foundation pit supporting water-stop pile.

The invention has the following beneficial effects:

one is as follows: the low-strength low-permeability concrete provided by the invention not only maintains the low-strength characteristic of the concrete, but also has lower water permeability, is suitable for a water-stopping pile, and obviously improves the low water permeability of the water-stopping pile.

The second step is as follows: in the preparation method of the low-strength low-permeability concrete, the material capable of obviously improving the service performance of the concrete is clay, the clay is common soil, the price is low, the materials are easily obtained, and the construction cost is obviously reduced; meanwhile, the use of clay does not influence the strength of concrete and still meets the strength performance of the concrete.

And thirdly: in the preparation method of the low-strength low-permeability concrete provided by the invention, the used materials do not need coarse aggregate, namely, stones and the like do not need to be used as concrete materials, the preparation process is simple, the construction operation is convenient, the construction time can be saved and the construction cost can be reduced in large-volume foundation pit engineering.

Fourthly, the method comprises the following steps: the low-strength low-permeability concrete provided by the invention has a good core pulling effect after being applied to a water stop pile, is small in occlusion difficulty, can occlude a pile for two days on average, is high in drilling core pulling continuity, and is less in pile bottom sediment.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is a schematic core drawing diagram of a water stop pile in a preparation method of low-strength low-permeability concrete provided in embodiment 1 of the present invention.

Fig. 2 is a schematic core-pulling diagram of a water stop pile of the preparation method of the low-strength low-permeability concrete provided by comparative example 1 of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

In the description of the present invention, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or to imply that the number of technical features indicated is significant. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

The method for preparing the low-strength low-permeability concrete of the embodiment of the present invention will be specifically described below.

A low-strength low-permeability concrete is characterized in that concrete mixture comprises cement, fly ash, clay, sand, water and a water reducing agent;

Further, the clay is clay with plasticity index more than 17; the plasticity index comprehensively reflects various important characteristics of the physical properties of the clay. The larger the plasticity index is, the finer the particles of the soil are, the larger the specific surface area is, the higher the content of clay or hydrophilic minerals of the soil is, and the larger the water content variation range of the soil in a plastic state is, that is, the plasticity index can comprehensively reflect the mineral components and particle size of the soil.

The clay in the invention is the clay with plasticity index more than 17, and the particle size of the clay can be ensured to meet the requirement of foundation pit engineering. During the hydration and coagulation of concrete, various components of the concrete mixture undergo a series of physicochemical changes. After the concrete is finally set, various micro bubbles and cracks exist in the concrete. In addition, because of insufficient construction vibration, a plurality of micro cracks often exist in the concrete, and the water permeability of the concrete is influenced. The clay is clay with plasticity index larger than 17, the clay particles are small, and after the concrete is mixed, the clay particles are mixed in micro cracks and micro bubbles between sand and a cementing material, so that various cracks invisible to human eyes in the concrete are compacted by the clay; meanwhile, the active ingredients in the clay can also react with other concrete admixtures chemically, so that the performance of the concrete is well improved, particularly the compactness of the concrete is well improved, and the concrete added with the clay has better impermeability.

But the clay content can obviously affect the strength of the concrete and can be adjusted according to the requirements of specific engineering. The concrete strength is lower when the clay content is more, and the workability of the concrete is also reduced, so that the engineering requirements cannot be met; the lower the clay content, the poorer the impermeability of the concrete, and in particular, the poorer the impermeability of low-strength concrete.

Further, the cement is slag portland cement with the strength grade of 32.5; the cement plays a role of a cementing material in the concrete, the higher the strength of the cement is, the more the dosage is, the higher the strength of the concrete is; conversely, the lower the strength of the cement, the lower the amount used, and the higher the strength of the concrete. Portland slag cement is divided into two types: one code number is: P.S.A, component: clinker and gypsum are more than or equal to 50 percent and less than 80 percent, and granulated blast furnace slag is more than 20 percent and less than or equal to 50 percent. And the other code number is as follows: P.S.B, component: the clinker and the gypsum are more than or equal to 30 percent and less than 50 percent, and the granulated blast furnace slag is more than 50 percent and less than or equal to 70 percent. Both types of portland slag cement can be used in the present invention. The slag portland cement has good water resistance and low hydration heat, and is suitable for underground engineering. Therefore, the portland slag cement is taken as a cementing material in the invention.

Further, the sand is medium sand; in the engineering, aggregate with the particle size of 0.15 mm-4.75 mm is used as fine aggregate, namely, sand. According to the thickness degree of the sand, the sand can be divided into coarse sand, medium sand and fine sand. The fineness modulus of the medium sand is 3.0-2.3, and the average grain diameter is 0.5-0.35 mm. The fineness modulus is an index of the fineness degree of the sand, the larger the fineness modulus is, the larger the particle size of the sand is, and conversely, the smaller the particle size of the sand is. The fine sand has small grain diameter, is suitable for low-permeability concrete, but has high manufacturing cost and is not suitable for engineering; in addition, the coarse sand has a large particle size and is not used in low-permeability concrete. Therefore, the medium sand is selected.

Further, the fly ash is F-class first-grade fly ash; fly ash with more than 10% CaO is called class C ash, while fly ash with less than 10% CaO is called class F fly ash. The C-class fly ash has certain hydraulicity and can be used as a cement admixture, and the F-class fly ash is often used as a concrete admixture and has lower hydration heat than the C-class fly ash during use. The concrete provided by the invention is mainly applied to the water-stop pile, belongs to mass concrete, has obvious hydration heat, and easily generates various micro cracks in the concrete due to the hydration heat, so the F-type fly ash with lower hydration heat is preferably selected.

In addition, the fly ash can be divided into a first-class fly ash, a second-class fly ash and a third-class fly ash according to fineness, wherein the first-class fly ash is the finest grade of particles, is usually used for underground concrete and underwater concrete, and is usually selected for concrete needing low density. The fly ash is used as the admixture of the concrete, can effectively change the workability of the concrete, simultaneously replaces a part of cement to play a role of a cementing material, and reduces the construction cost. The coal ash can enhance the compactness of concrete, active substances in the coal ash can chemically react with a cementing material, and meanwhile, micro particles in the coal ash can fill up micro cracks in the concrete, so that the compactness of the concrete is improved.

Furthermore, the water reducing agent is a polycarboxylic acid high-performance water reducing agent, the water reducing rate is not lower than 30%, the gas content is low, and the plastic-retaining performance is good. The polycarboxylic acid high-performance water reducing agent has low mixing amount and high water reducing rate, and is a cement dispersing agent commonly used for concrete. The water reducing agent is used to effectively reduce the water consumption, and the reasonable addition of the water reducing agent can obviously reduce the shrinkage of concrete and obviously improve the volume stability and durability of the concrete. The clay is used as an additive for the concrete provided by the invention, the clay needs more water to dissolve, and more water consumption is needed according to a conventional method, so that the strength of the concrete is obviously reduced and the concrete does not meet the requirements, and therefore, the use of the water reducing agent is very important.

The invention also provides a preparation method of the low-strength low-permeability concrete, which comprises the following steps:

s2: in order to fully and uniformly mix all the components during stirring, before stirring, beating massive clay into blocks with the particle size of less than 50mm, taking out 15-20% of the inner wall of the stirrer, adding the weighed clay and sand into the stirrer, and stirring for 30-40 s; wetting the inner wall of a stirrer by water, so that the mixture is not easy to stick to the inner wall when the mixture is added at the later stage, pouring clay and sand into the stirrer, uniformly stirring, then adding cement and fly ash, then adding 50-60% of water, and stirring for 40-60 s; at the moment, no water reducing agent is added, the mixture has high consistency and is difficult to stir, and then the water reducing agent and the rest water are added and stirred for 120-150 s;

s3: taking out part of the mixture and putting the mixture into a slump bucket to measure the slump; if the slump is less than 100mm, increasing the using amount of water in the original proportion, and correspondingly adjusting the using amount of the rest of the mixture; if the slump is larger than 150mm, reducing the using amount of water; if the slump is between 100 and 150mm, taking out the mixture for mold filling and maintenance, maintaining for 28 days under standard maintenance conditions, and measuring the compressive strength of the mold filling test block;

slump mainly reflects the workability of concrete, and the workability refers to whether the concrete is easy to construct and operate and the performance of uniform and dense, wherein the workability includes the fluidity, the cohesiveness and the water-retaining property of the concrete. If the slump is too large, the fluidity of the concrete is good, but the cohesiveness is poor, and if the slump is too small, the fluidity of the concrete is small, so that the construction is difficult, and the mixing compactness of the concrete is influenced. The slump range adopted by the invention is kept between 100mm and 150mm, so that the fluidity and cohesiveness of the concrete can be ensured, the construction is convenient, and the slump is beneficial to the compactness of the concrete after hydration and condensation.

Example 1

The embodiment provides a low-strength low-permeability concrete, and a preparation method thereof is as follows:

s1: mixing 60 liters of concrete in a test way, and weighing the cement components: fly ash: clay: sand: water: a water reducing agent;

s3: taking out part of the mixture and putting the mixture into a slump bucket to measure the slump; and (3) when the slump is between 100 and 150mm, taking out the mixture for mold-filling maintenance, maintaining for 28 days under standard maintenance conditions, and measuring the compressive strength of the mold-filling test block, wherein the compressive strength is qualified.

The weight ratio of the various admixtures in step S1, per cubic meter of concrete, is given in Table 1:

TABLE 1 concrete mix proportions used in example 1

Wherein the cement is slag portland cement of 32.5; the fly ash is F-class first-grade fly ash; the sand is medium sand; the water reducing agent is a polycarboxylic acid high-performance water reducing agent with the water reducing rate of not less than 30 percent; the clay is the clay with plasticity index more than 17; the water is tap water.

The compressive strength of 6 groups of concrete test blocks with sides of 100X 100mm were tested according to the mixing ratio, each group containing 3 test blocks, of which 3 groups were used for testing the compressive strength for 3 days and the other 3 groups were used for testing the compressive strength for 7 days. Table 2 gives the compressive strength values of the concrete test blocks in the 3-day age:

TABLE 2 compressive Strength of 3-day-old concrete used in example 1

Table 3 gives the compressive strength values of concrete test blocks with a side length of 100 × 100 × 100mm in the 7-day age:

TABLE 3 compressive Strength of 7-day-old concrete used in example 1

f_n-the intensity of an age of n days needs to be estimated;

f_a-measuring the intensity at age a days;

n is the number of days of age for which the intensity is to be calculated;

a-days of known age intensity;

observing that the early strength of the concrete in the tables 2 and 3 is relatively stable, converting the strength of the 7-day age in the table 3 into the 28-day compressive strength according to the formula, and considering the conversion into the standard cube strength, namely the cube test block with the side length of 150 × 150 × 150mm, the compressive strength of the standard cube test block can be obtained by multiplying 15.4Mpa by the conversion coefficient of 0.95, and the requirement of the concrete strength used by the water stop pile is met.

In addition, the impermeability of the concrete test block needs to be tested, and the impermeability test of the concrete requires the test block which uses a standard test block and has the maintenance age of more than 28 days. The impermeability grades of concrete are divided into six grades, i.e. P4, P6, P8, P10, P12 and more than P12, according to the maximum water pressure which can be borne by the concrete specimen in the impermeability test specified in GB50164 "concrete quality control Standard", which means that each grade can resist hydrostatic pressures of 0.4, 0.6, 0.8, 1.0, 1.2MPa and above without water permeability. The concrete impermeability test has 6 test pieces, and the maximum water pressure when 4 test pieces do not have water seepage represents the impermeability grade. The concrete with the impermeability grade being more than or equal to P6 is called impervious concrete, and the impermeability water pressure is 0.6 MPa.

This example provides 6 standard test blocks of 150X 150mm side length, and the maintenance age is 66 days, and the impermeability rating of 6 test blocks is determined. Table 4 gives the impermeability data for the 6 test blocks of this example:

TABLE 4 impermeability test used in example 1

As can be seen from the observation of Table 4, the maximum water penetration height of the 6 test blocks in this example 1 is 44mm, which meets the requirement of the 6 test blocks that the final water pressure of the water that is not penetrated by 4 (or more) test blocks is 0.6 MPa. The 6 test blocks in the embodiment can meet the requirement of no water seepage under the water pressure of 0.6MPa, and meet the requirement of P6-grade impervious concrete.

The concrete of this embodiment can be applied to among the stagnant water stake, and the stagnant water stake setting is in the middle of the fender pile. During construction, a water-stopping pile is constructed firstly, wherein the water-stopping pile is a plain concrete pile and is not provided with a reinforcement cage; and (3) constructing a fender pile, wherein a reinforcement cage is arranged in the fender pile, and the fender pile is arranged between two adjacent water stop piles. The water-stopping piles and the enclosure piles are constructed by using a casing drilling machine, after a small part of concrete of the adjacent water-stopping piles is cut, the concrete of the enclosure piles is poured, and the concrete of the enclosure piles is meshed with the concrete of the water-stopping piles, so that the water-stopping piles and the enclosure piles are seamlessly connected, and the water-stopping effect is achieved.

Referring to the attached drawing 1, the concrete provided by the embodiment is applied to an average 2-day occluded pile in a water stop pile, so that the construction is convenient, the continuity of drilling and coring is good, the forming quality is good, and the bottom sediment is less. The core is got in drilling of pile foundation is in order to detect the shaping quality condition of pile body concrete, for example the cementation condition of concrete, the inside has the compactness of no air vent, concrete and whether have the condition such as disconnected stake, and the core is got in drilling in addition and can be fine the sediment condition of looking over the pile bottom.

Example 2

This example provides a low strength, low permeability concrete having the following composition weight per cubic meter of concrete as shown in table 5:

TABLE 5 concrete mix proportions used in example 2

The other operations were the same as in example 1.

Reduce cement and sand quantity in this implementation, increased fly ash and clay quantity. By adjusting the using amount of each mixture, the concrete prepared according to the mixing proportion in the embodiment is applied to the water-stopping pile, and through a drilling coring test on the water-stopping pile, the coring effect is good, the coring continuity is good, and the core breaking and the slag deposition are less; and when the casing drill is used for construction and engagement, the pile is engaged in 2 days on average, which is beneficial to construction.

Example 3

The embodiment provides low-strength low-permeability concrete, and the weight of each cubic meter of the components is shown in table 6 according to the weight ratio of various concrete mixture materials:

TABLE 6 concrete mix proportions used in example 3

The mix proportion that this embodiment provided has fine effect after being used for the stagnant water stake of concrete that prepares, and the drilling of stagnant water stake is got the core continuity good, and disconnected stake and sediment are few, and when stinging the construction with the casing drill, on average 2 days sting a root stake, are favorable to the construction.

Comparative example 1

Comparative example 1 was provided for the purpose of distinguishing from the preferable blending ratios in examples 1 to 3. The weights of the various admixtures per cubic meter of concrete in comparative example 1 are given in Table 7:

TABLE 7 concrete mix proportions used in comparative example 1

The other operations were the same as in example 1.

Table 7 provides the concrete mix proportion of comparative example 1, refer to fig. 2, after the mix proportion that provides in comparative example 1 was used for the stagnant water stake, the result of coring of drilling was superior to the mix proportion that embodiment 1 ~ 3 provided, and the core continuity of drilling is fine, and nearly no disconnected stake and sediment, but the interlock degree of difficulty to the stagnant water stake is big, and on average 4 days interlock a stake, interlock efficiency of construction is very low, and the construction cycle is long, is not suitable for in the actual engineering.

Comparative example 2

Comparative example 2 is provided for the purpose of distinguishing from the compounding ratios in examples 1 to 3. The weight of each of the various admixture materials per cubic meter of concrete in comparative example 2 is shown in Table 8:

TABLE 8 concrete mix proportions used in comparative example 2

The other operations were the same as in example 1.

Table 8 provides the concrete mixing ratio of comparative example 2, the concrete prepared by the mixing ratio provided in comparative example 2 has poor workability, the pile after being used for the water stop pile has poor molding quality, the drilling coring continuity is poor, and the sediment in the pile is large, so that the concrete is not suitable for practical engineering.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made to the present invention by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The utility model provides a low strength low permeable concrete which characterized in that: the concrete mixture comprises cement, fly ash, clay, sand, water and a water reducing agent;

the concrete mixture comprises the following components in percentage by mass: cement: fly ash: clay: sand: water: (ii) a water reducing agent (82.9-117): (175.6-210.7): (1118-1235.2): (527-643.9): (320-330): (17.2-17.6), wherein the total mass of each cubic concrete mixture is 2300-2400 kg;

the preparation method of the concrete comprises the following steps:

s4, if the compressive strength is between 10 and 20Mpa, preparing the required concrete according to the dosage of each component determined in the step S1;

the water reducing agent is a polycarboxylic acid high-performance water reducing agent, and the water reducing rate is not lower than 30%;

the clay is clay with plasticity index more than 17.

2. The low-strength low-permeability concrete according to claim 1, wherein the cement is slag portland cement with a strength grade of 32.5.

3. The low strength low permeability concrete of claim 1, wherein the sand is medium sand.

4. The low strength low permeability concrete of claim 1, wherein said fly ash is class F first grade fly ash.

5. Use of the low-strength low-permeability concrete according to any one of claims 1 to 4 in the manufacture of a retaining pile for a foundation pit support.