A curing agent for curing high water content sludge soft soil in situ

Abstract

The present application relates to a kind of solidifying agent for in-situ solidification of high water content sludge soft soil, which is composed of sulphoaluminate cement 30-70%, alkali-activated cementitious material 20-60%, magnesium cementitious material 3-12% and surfactant 0-0.1% by mass percentage.The present application solves the problem of early strength development of solidified sludge soil under film curing conditions by compounding each component, and further overcomes the problem that existing solidifying agent cannot meet the on-site solidification bearing capacity due to the huge difference between indoor solidification strength and on-site solidification effect.The present application has the advantages of high solidification strength, short time, low cost and stable performance.For sludge soft soil with water content greater than 60%, considering the solidification strength under film curing conditions, it is suitable for in-situ solidification requirements on site, and can effectively improve the bearing capacity of soft soil foundation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of civil construction materials, and particularly relates to a solidifying agent for solidifying high-water-content silt soft soil in situ, which meets the in-situ solidification disposal. BACKGROUND

[0002] In recent years, the infrastructure construction in China has developed rapidly, and often faces soft soil foundations such as silt, silt soil, peat and peat soil. The soft soil has large natural water content, low strength, large void ratio and high compression coefficient, and has special engineering properties such as thixotropy and creep, and is often in a fluid-plastic or soft-plastic state. The engineering geological conditions are poor, and if no reinforcement treatment is performed, safety accidents such as ground subsidence cracking, foundation pit collapse or overturning often occur, which brings great challenges to project construction and engineering quality. Therefore, reinforcement measures must be taken according to the engineering properties of the soft soil.

[0003] Among many soft foundation disposal methods, the solidification and stabilization technology is an effective method, especially for in-situ silt solidification disposal, which has the advantages of saving transportation and disposal costs without silt transportation, saving construction costs without replacing stone slag, and reducing or completely replacing replacement soil. Chemical solidification has the advantages of wide raw material sources, low solidification cost and fast solidification time, and can achieve the effects of rapid hardening and cost saving, thereby creating favorable conditions for project construction.

[0004] Due to the high water content of soft soil, the indoor solidification strength and the in-situ solidification test results are often mismatched, which is difficult to guide the engineering practice. This mainly has two reasons. On the one hand, many studies dry, crush, sieve and remove impurities in the silt before solidification test (some also use static compaction method to prepare samples), which ignores the influence of initial water content on the solidification strength of silt, resulting in distorted test results. On the other hand, although the silt is used as is for solidification test, most tests use standard curing or non-film curing methods, while in fact, the external environmental conditions are also changing. For high-water-content silt, the internal water will accelerate the loss after mixing with the solidifying agent, thereby improving the solidification strength. At this time, it is difficult to judge the effectiveness of the solidifying agent, and the solidification results are also distorted. SUMMARY

[0005] The present curing agent for in-situ curing of high water content silt soft soil is prepared by considering the curing effect of high water content silt under film curing conditions, and solves the problem of early strength development of cured silt under film curing conditions by compounding various components, thereby overcoming the problem that the existing curing agent cannot meet the on-site curing bearing capacity due to the large difference between the indoor curing strength and the on-site curing effect, and effectively improving the bearing capacity of the soft soil foundation, solving the problem that the indoor curing strength and the on-site curing test results do not match, thereby meeting the demand for in-situ curing.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A curing agent for in-situ curing of high water content silt soft soil, the curing agent is composed of sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material, surfactant; the curing agent is composed of sulphoaluminate cement 30%-70%, alkali-activated cementitious material 20%-60%, magnesia cementitious material 3%-12%, surfactant 0-0.1% by mass percentage;

[0008] The alkali-activated cementitious material is composed of 65%-90% of cementitious component and 10%-30% of alkali activator by mass percentage;

[0009] The magnesia cementitious material is composed of 60%-75% of magnesium oxide and 10%-30% of magnesium chloride or magnesium sulfate by mass percentage;

[0010] The content of the surfactant is greater than 0;

[0011] The water content of the high water content silt soft soil is 60%-80%.

[0012] In the above technical scheme, the magnesia cementitious material is composed of 60%-75% of magnesium oxide and 10%-30% of magnesium chloride by mass percentage; or composed of 60%-75% of magnesium oxide and 10%-30% of magnesium sulfate.

[0013] Preferably, the sulphoaluminate cement is one or more of fast-hardening sulphoaluminate cement and low-alkalinity sulphoaluminate cement.

[0014] Preferably, the cementitious component in the alkali-activated cementitious material is one or more of blast furnace slag and high-titanium slag.

[0015] Preferably, the alkali activator in the alkali-activated cementitious material is one or more of sodium carbonate, sodium sulfate and sodium metaaluminate.

[0016] The magnesium cement is magnesia cement or magnesium sulpho cement; preferably, the magnesium oxide is light-burned magnesium oxide, and the content is greater than 75%.

[0017] Preferably, the magnesium chloride is anhydrous magnesium chloride, and the magnesium sulfate is anhydrous magnesium sulfate.

[0018] Preferably, the surface active agent is one or more of sodium dodecyl sulfate and sodium dodecyl benzene sulfonate.

[0019] The curing agent is prepared by mixing the sulphoaluminate cement, the alkali-activated cementitious material, the magnesium cement and the surface active agent in a corresponding mass ratio, uniformly, and grinding to 200 mesh or above, wherein the proportion of particles with a particle size of less than 10 microns is more than 30%.

[0020] The curing agent meets the curing strength of high-water-content silt soft soil under the condition of film natural curing, and is suitable for in-situ curing disposal in the engineering site.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The present application solves the problem of early strength development of silt soil under the condition of film curing by synergistically compounding the sulphoaluminate cement, the alkali-activated cementitious material, the magnesium cement and the surface active agent, thereby overcoming the problem that the existing curing agent cannot meet the in-situ curing bearing capacity due to the great difference between the indoor curing strength and the in-situ curing effect, and effectively improving the composite bearing capacity of the soft soil foundation.

[0023] Specifically, a proper amount of sulphoaluminate cement is added to fully utilize its characteristics of fast setting and hardening and high early strength, to quickly absorb and react under the condition of high-water-content film curing, thereby reducing the initial water content of silt. The alkali-activated cementitious material has excellent water resistance, and through the interaction between the cementitious component and the alkali activator, hydrated calcium silicate, hydrated calcium aluminate and hydrated calcium-alumino silicate gel phase substances are generated to fill and densify the silt curing body and improve the curing strength. Meanwhile, magnesium oxide and magnesium chloride or magnesium sulfate can harden relatively quickly at normal temperature and pressure to generate magnesium oxide-magnesium chloride / magnesium sulfate-water ternary compound crystalline phase, and through the composite trace anion surface active agent, the surface tension of the material can be reduced while introducing trace air during stirring, thereby strengthening the air hardening characteristics of the magnesium cementitious material and further improving the curing effect. Further, the specific surface area of the ground magnesium oxide is also larger, and the opportunity of contacting with the magnesium chloride or magnesium sulfate solution is also more, and the reaction is also better, and more crystalline phase is generated.

[0024] The application effectively improves the curing strength of high-water-content silt under the film curing condition by using four components of sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material and surfactant. The hydration product of sulphoaluminate cement is mainly ettringite, and if the dosage is too high, more products are generated in a short time, the micro-expansion side effect is highlighted, and the brittleness is large, which can easily cause the curing soil to crack and the strength to be reversed in the later period. In the case of using alkali-activated cementitious material alone, the high water content of silt leads to the decrease of alkali solubility, and the early strength of the cured silt soil is not high, and the use of sulphoaluminate cement can reduce the water content of silt, and the alkali-activated cementitious material generates more cementitious substances. Similarly, since the magnesium oxychloride cement or magnesium oxysulfate cement is air hardening, the use of magnesium oxychloride cement or magnesium oxysulfate cement alone cannot obtain the curing strength, and the dosage of surfactant can introduce part of air during stirring, weaken the air hardening characteristics of magnesium oxychloride cement or magnesium oxysulfate cement, promote the formation of crystalline phase, improve the curing strength, and meet the demand of in-situ curing.

[0025] The curing agent provided by the application has the advantages of high curing strength, short time, low cost and stable performance, and can meet the bearing capacity demand of in-situ curing. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The figure is a comparison of 3d compressive strength and 7d compressive strength of high-water-content silt cured by the curing agent of example 1 with and without film. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned objects, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the drawings. In the following description, many specific details are set forth in order to provide a thorough understanding of the application. However, the application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the scope of the application, so the application is not limited to the specific implementation disclosed below.

[0028] The application aims to provide a curing agent for in-situ curing of high-water-content silt soft soil, which is composed of sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material and surfactant.

[0029] Specifically, the curing agent is composed of 30%-70% of sulphoaluminate cement, 20%-60% of alkali-activated cementitious material, 3%-12% of magnesia cementitious material and 0-0.1% of surfactant by mass percentage;

[0030] The alkali-activated cementitious material is composed of 65%-90% of cementitious component and 10%-30% of alkali activator by mass percentage;

[0031] The magnesium cement is composed of 60-75% of magnesium oxide and 10-30% of magnesium chloride or magnesium sulfide by mass percentage;

[0032] The curing agent is composed of sulphoaluminate cement, alkali-activated cementitious material, magnesium cement and surfactant, which are mixed uniformly and ground to 200 mesh or more, wherein the particles with particle size less than 10 μm account for more than 30%.

[0033] The high water content silt soft soil has a water content of 60-80%.

[0034] Firstly, the silt curing strength under the conditions of coating and no coating is illustrated by using ordinary Portland cement composite blast furnace slag powder. Two kinds of silt soil samples with water content of 60% and 80% are selected for curing test, and the curing agent is ordinary Portland cement and blast furnace slag, wherein the blast furnace slag is 200 mesh and the calcium content is 42%. The mass ratio of cement to slag is 9:1, and the dosage of cement-slag in silt is 75 kg / m 3 , 100 kg / m 3 , 125 kg / m 3 . As shown in Table 1, the 3d and 7d compressive strength values of cement-slag cured silt under the conditions of no coating and coating are shown in the following table 1.

[0035] Table 1 Strength of cement-slag cured silt

[0036]

[0037] As shown in Table 1, the 3d and 7d compressive strength of cement-slag cured silt under the condition of no coating is higher than that under the condition of coating; the greater the age, the greater the strength difference; and the higher the water content of silt, the smaller the strength difference.

[0038] With the increase of the dosage of curing agent, the 3d and 7d compressive strength of cement-slag cured silt under the conditions of no coating or coating gradually increases. With the increase of the dosage of curing agent, the difference between the 7d compressive strength of cement-slag cured silt under the condition of coating and that under the condition of no coating is also greater.

[0039] The above results show that the strength of cement-slag cured silt under the conditions of coating and no coating is quite different, and the curing strength under the condition of no coating in the laboratory cannot be used as a reference for field curing. Therefore, the curing strength under the condition of coating needs to be considered to meet the demand of field in-situ curing strength.

[0040] Furthermore, the silt curing strength with and without coating is illustrated by using the magnesium oxysulfate cement composite alkali-activated cementitious material. The silt sample with a water content of 80% is selected for curing test, and the curing agent is composed of magnesium oxysulfate cement and alkali-activated cementitious material, and the curing agent dosage is 8.5%. Among them, the magnesium oxysulfate cement is composed of magnesium oxide and magnesium sulfate, and the magnesium sulfate is respectively composed of magnesium sulfate hexahydrate and anhydrous magnesium sulfate for comparison, and the alkali-activated cementitious material is composed of blast furnace slag, quicklime, sodium carbonate and sodium silicate, and the mass ratio is magnesium oxide: magnesium sulfate: blast furnace slag: quicklime: sodium carbonate: sodium silicate = 10:5:12:4:2:1. As shown in Table 2 below, the 7d and 14d compressive strength values of the silt cured by the magnesium oxysulfate cement composite alkali-activated cementitious material with and without coating.

[0041] Table 2 Silt strength cured by magnesium oxysulfate cement composite alkali-activated cementitious material

[0042]

[0043] The test results show that the silt cured by the magnesium oxysulfate cement composite alkali-activated cementitious material has no strength at 3d; for the magnesium oxysulfate cement with six water, the 7d strength without coating is 0.230MPa, the 7d strength with coating is 0.125MPa, the 14d strength without coating is 0.625MPa, and the 14d strength with coating is 0.320MPa; for the anhydrous magnesium oxysulfate cement, the 7d strength without coating is 0.295MPa, the 7d strength with coating is 0.205MPa, the 14d strength without coating is 0.760MPa, and the 14d strength with coating is 0.397MPa. Similar to the silt curing strength results of cement-slag, the 7d and 14d compressive strengths without coating are higher than those with coating; and the greater the age, the greater the strength gap. The results also show that the silt curing strength results of the magnesium oxysulfate cement composite alkali-activated cementitious material with and without coating are quite different, and the silt curing strength without coating in the laboratory cannot be used as a reference for field curing.

[0044] In the following examples and comparative examples, the silt is taken from a certain tidal flat silt stratum in the Greater Bay Area, and the measured initial water content is 70%, and the main clay mineral composition accounts for more than 40%.

[0045] Example 1

[0046] A curing agent for curing high water content silt soft soil in situ, which is composed of sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material and surfactant according to the following mass percentage: fast-hardening sulphoaluminate cement 40%, alkali-activated cementitious material 47.95%, magnesia cementitious material 12%, and sodium dodecyl sulfate 0.05%; wherein the alkali-activated cementitious material is composed of the following raw materials according to the following mass percentage: blast furnace slag 72.99%, sodium carbonate 8.24%, sodium sulfate 10.43%, and sodium metaaluminate 8.34%; and the magnesia cementitious material is composed of the following raw materials according to the following mass percentage: magnesium oxide 75% and anhydrous magnesium chloride 25%.

[0047] The sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material and surfactant are mixed uniformly according to the above mass ratio and ground to more than 200 mesh, wherein the particles with a particle size of less than 10 μm account for 50%, to obtain the final curing agent for curing high water content silt soft soil in situ.

[0048] The curing agent is mixed and stirred uniformly with high water content silt with a water content of 70% and then poured into a mold (size 70.7*70.7*70.7 mm), and the curing agent content is 7.8%. The test results show that the 3d average compressive strength of the cured test piece under room temperature natural curing with film is 0.86 MPa, and the 7d average compressive strength is 1.05 MPa; and the 3d average compressive strength of the cured test piece under room temperature natural curing without film is 0.95 MPa, and the 7d average compressive strength is 1.12 MPa.

[0049] Figure 1 is a comparison chart of the 3d compressive strength and 7d compressive strength of the high water content silt cured by the curing agent of Example 1 under the conditions of film covering and no film covering. Figure 1 It can be seen that, under the same conditions, the curing strength under the condition of film covering is basically equivalent to the strength under the condition of no film covering. Considering the on-site curing uniformity coefficient 0.5, the curing strength is still greater than 0.4 MPa, which can meet the bearing capacity requirement of on-site curing.

[0050] Example 2

[0051] A curing agent for curing high water content silt soft soil in situ, which is composed of sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material and surfactant according to the following mass percentage: fast-hardening sulphoaluminate cement 50%, alkali-activated cementitious material 37.92%, magnesia cementitious material 12%, and sodium dodecyl sulfate 0.08%; wherein the alkali-activated cementitious material is composed of the following raw materials according to the following mass percentage: blast furnace slag 65.93%, high-titanium slag 13.19%, sodium carbonate 6.33%, sodium sulfate 7.91%, and sodium metaaluminate 6.64%; and the magnesia cementitious material is composed of the following raw materials according to the following mass percentage: magnesium oxide 75% and anhydrous magnesium chloride 25%.

[0052] The sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material, and surfactant are mixed uniformly according to the above mass ratio and ground to 200 mesh or more, wherein the proportion of particles with a particle size of less than 10 μm is 40%, to obtain the final solidifying agent for solidifying high-water-content silt soft soil in situ.

[0053] The solidifying agent is mixed and stirred uniformly with high-water-content silt with a water content of 70% and then placed in a mold (size 70.7*70.7*70.7 mm), and the solidifying agent content is 7.8%, and the film is naturally cured at room temperature. Test results show that the 3d average compressive strength of the solidified test piece is 0.81 MPa, and the 7d average compressive strength is 0.98 MPa.

[0054] Example 3

[0055] A solidifying agent for solidifying high-water-content silt soft soil in situ is composed of sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material, and surfactant according to the following mass percentage: fast-hardening sulphoaluminate cement 55%, alkali-activated cementitious material 35.90%, magnesia cementitious material 9%, and sodium dodecyl sulfate 0.1%; wherein the alkali-activated cementitious material is composed of the following raw materials according to the following mass percentage: blast furnace slag 59.89%, high-titanium slag 19.50%, sodium carbonate 6.96%, sodium sulfate 6.96%, and sodium metaaluminate 6.69%; and the magnesia cementitious material is composed of the following raw materials according to the following mass percentage: magnesium oxide 66.67% and anhydrous magnesium chloride 33.33%.

[0056] The sulphoaluminate cement, alkali-activated cementitious material, magnesia cementitious material, and surfactant are mixed uniformly according to the above mass ratio and ground to 200 mesh or more, wherein the proportion of particles with a particle size of less than 10 μm is 35%, to obtain the final solidifying agent for solidifying high-water-content silt soft soil in situ.

[0057] The solidifying agent is mixed and stirred uniformly with high-water-content silt with a water content of 70% and then placed in a mold (size 70.7*70.7*70.7 mm), and the solidifying agent content is 7.8%, and the film is naturally cured at room temperature. Test results show that the 3d average compressive strength of the solidified test piece is 0.77 MPa, and the 7d average compressive strength is 0.92 MPa.

[0058] Comparative Example 1

[0059] A solidifying agent for solidifying high-water-content silt soft soil in situ is composed of PO42.5 cement. The cement is ground to a proportion of particles with a particle size of less than 10 μm of 35%, to obtain the final high-water-content silt soft soil solidifying agent.

[0060] The curing agent is mixed with high water content sludge with water content of 70% and stirred uniformly, and then is put into a mold (size 70.7*70.7*70.7mm), the curing agent content is 7.8%, and the film is naturally cured at room temperature. The test shows that the 3d average compressive strength of the cured test piece is 0.67MPa, and the 7d average compressive strength is 0.84MPa.

[0061] Comparative Example 2

[0062] A curing agent for curing high water content sludge soft soil in situ, which adopts magnesia oxychloride cement. The magnesia oxychloride cement is composed of 75% mass fraction of light burned magnesia and 25% mass fraction of anhydrous magnesium chloride, and the final curing agent for curing high water content sludge soft soil in situ is obtained by grinding the magnesia oxychloride cement to 50% of particles with particle size less than 10μm.

[0063] The curing agent is mixed with high water content sludge with water content of 70% and stirred uniformly, and then is put into a mold (size 70.7*70.7*70.7mm), the curing agent content is 7.8%, and the film is naturally cured at room temperature. The test shows that the 3d average compressive strength of the cured test piece is 0.67MPa, and the 7d average compressive strength is 0.84MPa.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Various technical features of the above-described embodiments can be combined in any manner, and to make the description concise, not all possible combinations are described, but it is understood that the application embraces all such possible combinations.

Claims

1. A solidifying agent for solidifying a high water content sludge soft soil in situ, characterized by, The curing agent is composed of raw materials in the following mass percentages: sulphoaluminate cement 30%-70%, alkali-activated cementitious material 20%-60%, magnesia cementitious material 3%-12%, and surfactant 0-0.1%. The alkali-activated cementitious material is composed of, in mass percentages, cementitious component 65%-90% and alkali activator 10%-30%; the sum of the cementitious component and the alkali activator is 100%. The magnesia cementitious material is composed of, in mass percentages, 60%-75% of magnesia and 10%-30% of magnesium chloride or magnesium sulfate; the sum of the magnesia and the magnesium chloride or magnesium sulfate is 100%. The content of the surfactant is greater than 0. The cementitious component is one or more of blast furnace slag and high-titanium slag. The alkali activator is one or more of sodium carbonate, sodium sulfate, and sodium metaaluminate. The surfactant is one or more of sodium dodecyl sulfate and sodium dodecyl benzene sulfonate. The high-water-content silt soft soil has a water content of 60%-80%.

2. The solidifying agent for solidifying soft soil of high water content in situ according to claim 1, characterized by, The sulphoaluminate cement is one or more of fast-hardening sulphoaluminate cement and low-alkalinity sulphoaluminate cement.

3. The solidifying agent for solidifying soft soil of high water content in situ according to claim 1, characterized by, The magnesia cementitious material is magnesia oxychloride cement or magnesia oxysulfate cement.

4. The solidifying agent for solidifying soft soil of high water content in situ according to claim 1, characterized by, The magnesia is light-burned magnesia with a content greater than 75%.

5. The solidifying agent for solidifying soft soil of high water content in situ according to claim 1, characterized by, The curing agent is composed of raw materials mixed uniformly in mass ratios and ground to more than 200 mesh, wherein the particles with a particle size less than 10 microns account for more than 30%.

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