RU2372445C2 - Method for cementation of weak soils - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention is related to the field of construction, in particular to methods for cementation of weak soils in preparation and reconstruction of buildings and structures foundations. In method of weak soils cementation, including preparation of water suspension of cement with finely dispersed mineral component and introduction of prepared suspension into soil, as finely dispersed mineral component they use carbonate sludge of chemical water treatment for boiler houses of heat power plants - HPP or heat power stations HPS, which is introduced in composition of solid phase of water suspension of cement prior to preparation of specified suspension in amount of 10-35 wt % of solid phase mass, identifying maximum value of its amount according to the following formula:

where W/C - water cement ratio of cement water suspension without addition of carbonate sludge that makes 0.44-0.86.

EFFECT: improved physical-mechanical characteristics of cement-containing solution intended for introduction into strengthened soil, expansion of raw material base of cementation mortars making and reduction of material and labour expenses in process of soil strengthening.

1 ex, 6 tbl

Description

The invention relates to the construction and can be used to strengthen soft soils in the preparation and reconstruction of the foundations of the foundations of buildings and structures.

A known method of cementation of soils, which consists in introducing into the soil through an injector or a drilled well a hardening solution based on Portland cement under a pressure of 0.1-0.5 MPa (see, for example, Rzhanitsin B. A. Chemical fixing of soils in construction. - M. : Stroyizdat, 1986).

By injection of cement-containing mortars, sand of medium size and large, pebble and gravel deposits, as well as fractured rock with a filtration coefficient of up to 200 m / day, are fixed. Depending on the type and structure of the fixed soil, the water-cement ratio (W / C) of these solutions can vary from 0.4 to 20 (Konyukhov D.S. Construction of shallow underground underground structures. - M.: Architecture-S, 2005). However, in practice, cement-water suspensions with a value of W / C = 0.5-1 (http://www.yurkevich.ru/3r7podr.php; http://www.new-ground.ru/ are used to fix incoherent soils) main / index.html? id = 4 & eid = 2). Cementation is used not only to improve the strength, deformation and antifiltration characteristics of the soil massif, but also to fill large voids under the soles of foundations, artificial underground workings, etc. Important advantages of cement mortars are the absence of environmental pollution, high mobility and a relatively short setting time.

At the same time, cement-water suspensions have low sedimentation stability. In addition, the compressive strength of cement-soil stone formed during injection of the fixing mortar is not high enough - up to 1-2 MPa (Kambefor A. Injection of soils. - M .: Energy, 1971). One of the reasons for the relatively low strength of the fixed soil mass is that the hardened cement matrix at those H / C values that are usually used in cement-water suspensions has significant porosity and is subject to shrinkage deformations and, therefore, has a tendency to crack formation (Dzhantimirov Kh.A., Yudovich B.E. et al. Improvement of geotechnical cementing materials based on hydraulic binders / Scientific works of the International Scientific Conference on Concrete and Reinforced Concrete. - Moscow: Deepak, 2005. V.3 p. 497-504).

To improve the quality of soil cementation, cement-sand mortars are used, but their use is effective only for rocks with a specific water absorption of at least 3 l / min (L. Goncharova, Fundamentals of Artificial Soil Improvement. - M.: Moscow State University, 1973). It is believed that, at lower values of water absorption, almost all the sand remains at the boundary of the massif being fixed, and therefore, only a cement-water suspension with a value of W / C> 1 still penetrates deep into the massif (Dzhantimirov H.A., Yudovich B.E. and others Improvement of geotechnical cementitious materials based on hydraulic binders / Scientific works of the International Scientific Conference on Concrete and Reinforced Concrete. - M .: Deepak, 2005. V.3, p.497-504).

As follows from the foregoing, in the method of cementing soft soils, including the introduction of a cementing mortar into the soil, the specified solution must have a sufficiently high penetrating ability at the smallest possible value of W / C, depending on the dispersion of the particles of the solid phase of the solution and its sedimentation stability. To implement these requirements, finely dispersed mineral components, for example, are introduced into the cement-water suspension: fly ash of thermal power plants (Kambor A. Soil injection. - M .: Energia, 1971), bentonite clays, finely ground limestones, sandstones and blast-furnace slags (Injection hardening rocks / Yu.Z. Zaslavsky, E.A. Lopukhin et al. - M .: Nedra, 1984), finely quartz sand (RU 2054502, 02.20.1996) and others.

However, the mechanical strength of the fixed soils obtained by introducing modified cement-water suspensions remains insufficiently high (4-5 MPa). One of the reasons for this is the insufficient strength of the grout. As laboratory studies of the strength properties of crushed igneous rocks injected with cement mortars showed, the tensile strength during uniaxial compression of rock samples decreases with increasing water-cement ratio of the injection mortar in the same way as the tensile strength of the mortar itself after curing (Injection hardening of rocks / Yu.Z. Zaslavsky, E.A. Lopukhin and others - M .: Nedra, 1984).

The closest in technical essence and the achieved result is a method of cementing soft soil, which involves injecting a fixing solution into the soil - an aqueous suspension of cement with a highly dispersed mineral filler, which is used as a microbiologically activated freshwater lake sludge in the following ratio of components, wt.%:

water suspension of cement 88-92 aqueous suspension of activated lake silt 8-12

(RU 2098554, E02D 3/12, 10/12/1997).

However, the mechanical strength of the cement-sand stone formed in the soil as a result of the injection of the fixing solution remains insufficiently high. In addition, obtaining microbiologically activated sludge requires a lot of time (24-30 hours) and complex technological equipment (for example, a thermostatic screw mixer), which complicates and increases the cost of soil consolidation.

The objective of the invention is to develop a method of cementing soft soils by introducing a fixing solution with increased sedimentation stability and mechanical strength into the soil, expanding the raw material base for the production of cementitious mortars and reducing material and labor costs when fixing soils by cementation.

The essence of the invention lies in the fact that in the method of cementing soft soils, including the preparation of an aqueous suspension of cement with a finely dispersed mineral component and introducing into the soil the prepared slurry, carbonate slurry of chemical water treatment is used as a finely dispersed mineral component for boiler plants of thermal power plants of thermal power plants or heat and power plants in thermal power plants, which are introduced the composition of the solid phase of an aqueous suspension of cement before preparing the specified suspension in an amount of 10-35 wt.% by weight of solid f basics, determining the maximum value of its quantity by the formula

where W / C is the water-cement ratio of an aqueous suspension of cement without the addition of carbonate sludge, comprising 0.44-0.86.

Characterization of raw materials

1. Portland cement. To implement the proposed method of cementation of soft soils, binder-free Portland cement M400 of the Novorossiysk cement plant "Proletary" was used as a binder. Its properties were determined according to the methods of GOST 310.1-76 "Cement. Test methods. General Provisions ”, GOST 310.2-76“ Cements. Methods for determining the fineness of grinding ", GOST 310.3-76" Cements. Methods for determining the normal density, setting time and uniformity of volume change ”, GOST 310.4-81“ Cements. Methods for determining bending and compression strengths. "

2. Fine mineral component. A carbonate slurry of chemical water treatment was used as a finely dispersed mineral component, which is a waste from production at thermal power plants or thermal power plants, is formed when softened with hydrated lime, river water taken for technological purposes, is precipitated and discharged into the dump as an aqueous suspension. The carbonate sludge contains mainly calcium carbonate CaCO ₃ (72-75%), magnesium hydroxide Mg (OH) ₂ , (5.0-5.5%), silicon oxide SiO ₂ (2.0-2.5%) as well as iron and aluminum oxides.

Tests of carbonate sludge were carried out in accordance with the criteria for assessing the properties of additives used in the manufacture of cement according to GOST 24640-91 “Additives for cements. Classification".

The test results of the starting materials are given in table 1.

Examples of the invention

1. Preparation of cement slurries and samples of cement slurry stone for mechanical testing

Technological parameters of cementing mortars: water-cement ratio W / C = 0.4-1.2, the content of carbonate sludge in the composition of the solid phase is 0-50%.

The dosed water, Portland cement and carbonate sludge were sequentially loaded into a 50-liter turbulent laboratory mixer with a rotor speed of 620 rpm and mixed for 3 minutes. The mobility of the solution was controlled by a viscometer and, if necessary, adjusted by adding water or solid components.

The prepared mixtures were poured into metal molds measuring 7.07 × 7.07 × 7.07 cm and kept for 28 days under normal conditions.

2. Determination of the properties of cementitious mortars Testing of cementitious mortars was carried out according to the methods:

- GOST 5202-86 “Building solutions. Test methods "- when determining mobility and compressive strength during cracking;

- GOST 310.6-85 “Cements. Methods for determining water separation ”- in determining water separation.

In addition, the mobility of the solutions was determined using a Suttard BC-1 viscometer (TU 25-06.393-80).

The analysis of the obtained experimental data was carried out in accordance with the provisions of GOST 24640-91.

3. Test results

3.1. To study the effect of carbonate sludge of chemical water treatment on the water separation of cementitious solutions, aqueous suspensions were prepared with various sludge contents mixed with cement: from 10 to 30%. The mass of the solid phase in all solutions was the same 350 g, and the water-solid ratio was 1. The compositions of cementitious solutions used in the inventive method of cementation of soft soils, and the values of their water separation are given in table 2.

From the presented data it is seen that carbonate sludge significantly reduces the water separation of suspensions. For example, the standard water separation of a cement-water suspension is 16.7%, and when part of Portland cement is replaced with carbonate sludge (10 wt.%), It decreased to 8.5% and then naturally decreased. The specific surface of carbonate sludge is 7800 cm ² / g, which is 2.44 times higher than the specific surface of cement. Thus, the average particle size of the sludge is significantly smaller than the particles of cement, as is the true density of this material, and therefore the addition of sludge slows the settling of cement particles in water. This allows in some cases to change the qualification of cement-containing injection solutions. So cement-water suspensions with C / B≤1.5 (B / C≥0.67) are classified as unstable solutions (Kambefor A. Injection of soils. - M .: Energy, 1971). According to our data, the water separation of the composition with W / C = 0.67 after 120 minutes is 9.0%, but when replacing part of the cement with carbonate sludge in an amount of 30 wt.%, It becomes equal to 1.8%, which is typical for stable injection solutions.

3.2. The mechanical strength of the samples of hardened cementitious mortars was measured after 28 days of storage under normal conditions. Table 3 presents the results of its measurement for compositions with W / C equal to 0.47. This water-cement ratio characterizes the properties of the cement stone formed by sequentially introducing the cementitious mortar components into the fixed soil described in the prototype method for fixing weak soils (RU 2098554). From table 3 it follows that in a wide range of concentrations of carbonate sludge, the strength of the cement stone formed during the hardening of cement-slurry water suspension, significantly exceeds the strength of the material of the prototype.

The possibility of increasing the mechanical strength of the hardened cementitious mortar was investigated by the authors of the present invention for other H / C values that are usually used in practice when fixing unbound soils - alluvial deposits and man-made arrays (bulk bases) when preparing construction sites (Tables 4, 5, 6 ) In these tables, the compositions of cementitious mortars are chosen so that they have the same mobility (for the compositions in Table 4, it corresponds to the mobility of a cement-water suspension with W / C = 0.4, and in Table 5 - the mobility of a cement-water suspension with B / C = 0.54, and in table 6 - the mobility of the cement-water suspension with B / C = 0.7).

For each composition containing an additive of carbonate sludge, its analogue is indicated - the composition of a cement-water suspension without adding sludge with the same W / C value as that of the claimed composition. In all cases considered, the tensile strength under uniaxial compression of the modified samples exceeds the strength of cement-water suspensions without the addition of carbonate sludge. As for other finely dispersed mineral components, an increase in mechanical strength can be associated with a decrease in the total porosity of the cement stone, as well as with the strengthening of the contact zone between the cement particles and the mineral component of a certain chemical composition (Additives in concrete: Ref. Manual / V.S. Ramachandran , R.F. Feldman and others. - M .: Stroyizdat, 1988). In our case, both of these factors act simultaneously. Indeed, the average particle size d of carbonate sludge particles (d≈3 μm) is significantly smaller than cement, and calcite is the main mineral of carbonate sludge. Therefore, intergranular (d> 10 μm) pores and partially inter-microaggregate (10≤d <1 μm) pores in the cement stone will be filled with the addition of carbonate sludge, and the interaction of cement minerals with calcite during cement hydration leads to the formation of calcium hydrosilicates of high basicity, which the edges of the [Si ₂ O ₇ ] ⁶ radical are commensurate with the edges of the unit cells of calcite and calcium hydroxide, which ensures high strength of the cement-slurry composition (L. Goncharova, Fundamentals of Artificial Soil Improvement. - M.: Moscow State University, 1973).

The results of the measurements in tables 4, 5 and 6, the authors of the invention provide because, firstly, the H / C value used for the cement slurry used in the prototype is not, in our opinion, optimal for the selected composition of the fixed soil - coarse sand according to GOST 8736-93 (the description of the prototype invention indicates that the content of the fraction with a particle diameter of 1-0.5 mm in sand is 3%, 0.5-0.25 mm 60%, 0.25-0.1 mm 32% and 0.1 0.05 mm - 5%). According to other sources (DS Konyukhov, Construction of shallow underground urban structures. - M.: Architecture-S, 2005), cement-water suspensions with significantly higher W / C values are used for such fixed soils.

Secondly, the results of testing the properties of cementitious mortars at various H / C values allow us to establish the limiting (minimum and maximum) values of the carbonate sludge content at which the cement stone strength increases. The minimum concentration of carbonate sludge in the composition of the solid phase of the solution is the same for all W / C values and is 5 wt.% (Table 4, example 1, table 5, example 1, table 6, example 1). With a lower content of carbonate sludge, an increase in mechanical strength is insignificant and does not meet the criterion of GOST 24640-91. The highest content of carbonate sludge (35 wt.%) In the composition of the carbonate sludge, given in the formula of the invention, was obtained for the initial solution with W / C = 0.4 (table 4, example 5), which is the minimum possible for injection cement-containing solutions (Goncharova L.V. Fundamentals of artificial soil improvement. - M.: Moscow State University, 1973). With a higher content of carbonate sludge, an increase in mechanical strength compared to a solution with the same W / C value that does not contain additives becomes insignificant (Table 4, examples 6, 7).

The established limits for the content of carbonate sludge (5-35 wt.%) In the composition of the solid phase of the cement slurry at the lowest possible water content (W / C = 0.4) thereby determine the limits of the content of each component in the composition of the cement slurry:

Portland cement 41.7-66.9 carbonate sludge 3.4-22.3 water rest

(see table 4). When the cement content is more than 66.9 wt.%, The relative carbonate sludge content decreases beyond the established limit (5 wt.%), And, as was shown, the increase in the strength of the cement stone becomes insignificant. The minimum cement content (41.7 wt.%) In equidistant solutions with an initial value of V / C = 0.4 (Table 4, Example 5) is determined by the maximum possible carbonate sludge content in relation to cement (35 wt.%).

A large number of experimental data obtained allows us to propose a mathematical formula that determines the maximum concentration C _m (in wt.%) Of carbonate sludge for each value of the H / C solution, at which the mechanical strength of the hardened cement mortar increases compared to the similar cement-water composition suspensions:

where W / C is the water-cement ratio of the cement-water suspension.

For example, for B / C = 0.4 C _m = 35 wt.%, For B / C = 0.54 C _m = 25.2≈25 wt.%, For B / C = 0.7

With _m = 14 wt.%, Which corresponds to experimental data.

This formula can be used not only in determining the composition of injection cement mortars, but also in other types of cement-containing materials, in particular mortars and concrete.

The positive effect of the use of the invention consists, firstly, in increasing the mechanical strength of the fixed soil mass, which leads to lower production costs for fixing the soil of the bases, as it allows to reduce the amount of solution introduced into the soil and, therefore, the time of this technological operation. In addition, as follows from the results obtained (table 4, example 2 and table 3, example 4; table 6, example 2 and table 5, example 5; table 6, example 6 and table 4, example 7 ), in cases where injection solutions prepared without the addition of carbonate sludge and in which part of the cement is replaced with carbonate sludge have the same strength, the cement savings can be from 12 to 15 wt.%. Reducing cement consumption and expanding the raw material base for the production of fixing mortars opens up new opportunities for the implementation of geotechnical works in construction.

Finally, the use of carbonate sludge as part of injection solutions is one of the solutions to the important problem of utilization of technogenic waste from energy enterprises.

Claims (1)

A method of cementing soft soils, including the preparation of an aqueous suspension of cement with a finely dispersed mineral component and introducing the prepared slurry into the soil, characterized in that carbonate slurry of chemical water treatment is used as a finely dispersed mineral component for boiler plants of thermal power plants — TPPs or heat and power plants — TPPs, which are introduced into the composition of solid phase of an aqueous cement suspension before preparing the specified suspension in an amount of 10-35 wt.% by weight of the solid phase, determining the poppy imalnoe value of its quantity by the formula

where W / C is the water-cement ratio of an aqueous suspension of cement without the addition of carbonate sludge, comprising 0.44-0.86.