CN111205006A

CN111205006A - Bentonite modified cement and preparation method thereof

Info

Publication number: CN111205006A
Application number: CN202010031477.1A
Authority: CN
Inventors: 唐国旺; 王贵和; 贾苍琴; 锁扬洋; 刘耀
Original assignee: China University of Geosciences Beijing
Current assignee: China University of Geosciences Beijing
Priority date: 2020-01-13
Filing date: 2020-01-13
Publication date: 2020-05-29
Anticipated expiration: 2040-01-13
Also published as: CN111205006B

Abstract

The invention relates to bentonite modified cement and a preparation method thereof, wherein the bentonite modified cement comprises modified cement and a microbial inoculum, the preparation method of the bentonite modified cement comprises the step of mixing the modified cement with the microbial inoculum, the modified cement comprises bentonite and portland cement, and the microbial inoculum contains bacillus pasteurii. The invention develops a new method, insists on using the bentonite to modify the cement and enhances the strength of the cement by utilizing biomineralization; the invention also optimizes the technological parameters. The bentonite modified reinforced cement has great application value, can ensure the reutilization of industrial byproducts, simultaneously reduces the consumption of the cement, and does not generate pollutants.

Description

Bentonite modified cement and preparation method thereof

Technical Field

The invention relates to modified cement, and belongs to the technical field of biological building materials.

Technical Field

Population growth and accelerated urbanization increase the consumption of cement because cement is inexpensive and readily available. However, carbon dioxide discharged during cement production and environmental damage caused by cement production raw materials cause global warming, and heavy pressure is generated to reduce cement consumption. The use of environmentally friendly auxiliary materials to partially replace cement can reduce cement consumption. These environmentally friendly auxiliary materials may be industrial by-products, or naturally available materials, which require relatively little energy to manufacture.

The compressive strength of concrete is an important factor affecting its durability and is an important characteristic of cement. Therefore, it would be very valuable to identify a suitable technique for ensuring the mechanical properties of the structure, while at the same time partially replacing the cement with supplementary materials. At present, most of mortar samples researched are researches on replacing cement by fly ash and the like, the researches on partially replacing the cement by bentonite are few, and the bentonite is generally considered not to be too much, otherwise, the compressive strength of the cement is seriously influenced. The bacteria induced calcium carbonate precipitation is a novel biomineralization product discovered in recent years and widely used for improving the durability of cement, and a usable bacterium is bacillus pasteurianus (Sporosarcina pasteurii), but the properties of bentonite are complex, and the interaction mechanism with bacteria is not clear enough.

Disclosure of Invention

The invention develops a new method, insists on modifying the cement by using the bentonite, ensures the strength of the cement, and has stronger strength than the cement without adding the pasteurella.

The method comprises the step of mixing modified cement and a microbial inoculum, wherein the modified cement comprises bentonite and portland cement, and the microbial inoculum contains bacillus pasteurianus.

Preferably, the modified cement consists of sodium bentonite and ordinary portland cement, wherein the weight percentage of the sodium bentonite is 10-40%; the volume mass ratio of the microbial inoculum to the modified cement is 1.5L: 1Kg, the pasteurella is pasteurella ATCC11859, and the using amount of the ATCC11859 bacteria is OD₆₀₀1-2 of 1/4 for the amount of bacteria in an aqueous solution of ATCC11859, the OD measured at room temperature against water, and the distance light travels in the sample may be 1 cm.

Preferably, the OD of the aqueous solution of ATCC11859 bacteria₆₀₀The weight percentage of the bentonite in the modified cement is 20 percent.

Preferably, the microbial inoculum also contains calcium ions and urea, and optionally, the weight percentage of bentonite in the modified cement is 10-20%, 20-30% or 20-40%.

Preferably, the OD of the aqueous solution of ATCC11859 bacteria₆₀₀Is 1-1.5 or 1.5-2.

Preferably, the molar amounts of the calcium ions and the urea are the same, such as the concentrations are both 0.375 mol/L.

Preferably, the calcium ions are provided in the form of calcium chloride.

Preferably, the microbial inoculum is in the form of an aqueous solution, for example, a mixed aqueous solution containing 0.5mol/L calcium chloride and 0.5mol/L urea is mixed with the ATCC11859 bacterial solution in a volume ratio of 3:1 to obtain the microbial inoculum. As a further preference, the aqueous solution of the Bacillus pasteurianus ATCC11859 strain is prepared as follows: inoculating Paenibacillus pasteurii ATCC11859 into suspension culture medium, culturing at 120 rpm in 30 deg.C culture medium for 48 hr, centrifuging the obtained bacterial suspension at 4 deg.C for 8 min to granulate bacteria, resuspending the bacterial granules in 1000ml deionized water, and diluting the bacteria to 600nm (OD)₆₀₀) Has an optical density of 1.0 to 2.0, preferably OD₆₀₀Is 2.0. Optionally, the suspension medium has a formulation of: casein peptone (15g/L), soybean peptone (5g/L), NaCl (5g/L), urea (20g/L), deionized water to constant volume, adjusting pH to 7.3, and sterilizing at 121 deg.C for 30 min.

Preferably, the chemical composition of the bentonite is shown in the detailed embodiment table 1.

Preferably, the chemical composition of the portland cement is shown in table 1 of the detailed embodiment.

As an example, a bentonite-modified cement is prepared, which comprises:

1) preparation of a bacillus pasteurii suspension: inoculating the pasteurella bacillus ATCC11859 into a suspension culture medium, culturing for 48 hours in the culture medium at the temperature of 30 ℃ at the rotating speed of 120 revolutions per minute, centrifuging the obtained bacterial suspension at the temperature of 4 ℃ for 8 minutes to granulate the bacteria, re-suspending the bacterial granules in 1000 milliliters of deionized water, and diluting to obtain the pasteurella bacillus suspension;

2) preparing a reaction solution: respectively preparing 0.5mol/L calcium chloride and 0.5mol/L urea, and then mixing the calcium chloride and the urea in equal volumes to obtain reaction liquid;

3) preparation of a modification solution: uniformly mixing the bacillus pasteurii suspension in the step 1) and the reaction liquid in the step 2) to obtain a modified solution, wherein the volume ratio of the bacillus pasteurii suspension to the reaction liquid is 1: 3;

4) preparing modified cement: weighing bentonite and portland cement according to a weight ratio, wherein the bentonite and the portland cement comprise the following components in percentage by weight:

bentonite: 10 to 40 percent of

Portland cement: 60% -90%;

5) mixing the modified cement prepared in the step 4) with the modified solution prepared in the step 3) according to the weight-to-volume ratio (KG/L) of 1:1.5 to obtain the bentonite modified reinforced cement.

OD of the Bacillus pasteurianus suspension in the step 1)_{600 may be}1.0-2.0; the weight percentage of the bentonite and the portland cement in the step 4) can be as follows:

bentonite: 20 percent of

Portland cement: 80 percent.

The invention also discloses bentonite modified cement corresponding to any one of the methods.

The invention develops a new method, insists on modifying cement by using bentonite, and enhances the strength of the cement by using the biological mineralization of the bacillus pasteurii; the invention also optimizes the technological parameters. The bentonite modified reinforced cement has great application value, can ensure the reuse of industrial byproducts, simultaneously reduces the consumption of the cement, and does not produce pollutants.

Drawings

FIG. 1 is a comparison of the strength tests of Experimental example 1.

FIG. 2 is a comparison of the strength tests of Experimental example 2.

FIG. 3a is a comparison of strength tests for each sterile control sample of Experimental example 3; FIG. 3b is a comparison of the strength test of each bacteria-containing cement of Experimental example 3.

FIG. 4 is a graph showing the particle size distribution of a raw material bentonite used in each experimental example in the embodiment.

FIG. 5 is a graph showing the particle size distribution of Portland cement used in each experimental example in the detailed description.

Detailed Description

The following experiments are intended to further illustrate the present invention, but they are not intended to limit or restrict the scope of the present invention.

B, bacillus pasteurii: ATCC11859, purchase.

Preparation of suspension medium: casein peptone (15g/L), soybean peptone (5g/L), NaCl (5g/L) and urea (20g/L) were added to 1000mL of deionized water, respectively, adjusted to pH 7.3, and sterilized at 121 ℃ for 30 minutes.

Urea and calcium chloride (CaCl) for use in the invention₂) Sodium chloride (NaCl), casein peptone and soybean peptone were purchased from Shanghai pharmaceutical controlled chemical reagents, Inc. in China, and model 752 UV-visible spectrophotometer was purchased from Shanghai Shunhui scientific instruments, Inc.

Bentonite was supplied by Shicheng Automation Co., Ltd, Leqing, and the average particle size (D) of sand₅₀) The particle size distribution curve of the bentonite is 13.89 mu m, and is shown in figure 4; the use of ordinary portland cement conforming to IS 12269-1987, provided by Union-dam Cement, Inc. in Texas, wherein the cement grading size distribution curve IS shown in FIG. 5, the average particle size (D) of the sand₅₀) It was 17.04. mu.m. The chemical composition of the cement and bentonite is shown in table 1.

TABLE 1

Oxide	Bentonite (mass%)	Cement (mass%)
			CaO	2.624	55.52
SiO₂	71.265	24.55
			Al₂O₃	14.462	8.24
Fe₂O₃	3.58	4.44
			SO₃	0.021	3.34
MgO	2.449	2.19
			K₂O	2.158	0.81
TiO₂	0.364	0.49
			Na₂O	2.849	0.30
MnO	0.088	0.13

The method for testing the compressive strength comprises the following steps: according to the requirements of IS 4031-1988, a 70.6mm cubic mold was used. All test pieces are demoulded and then placed in a room at 25 ℃ for curing until compressive strength tests are carried out on

days

3, 7 and 28. And carrying out unconfined compressive strength test by adopting an automatic compression tester.

Preparation of a bacillus pasteurii suspension: the Pasteurella pasteurii ATCC11859 was inoculated into 100L of suspension medium, cultured at 120 rpm in 30 ℃ medium for 48 hours, the resulting bacterial suspension was centrifuged at 4 ℃ for 8 minutes to granulate the bacteria, and the bacterial granules were suspended in 10L of deionized water for dilution.

Preparation of bacterial suspensions at different concentrations: 2L of each of the above-mentioned Bacillus pasteurianus ATCC11859 suspensions was taken, and the OD thereof was diluted with deionized water₆₀₀0.5, 1.0, 1.5 and 2.0 respectively for use, wherein the OD is detected by the following method:

adjusting the wavelength of an ultraviolet-visible spectrophotometer to 600nm, taking water as a control sample, detecting the OD value of a bacterial liquid at room temperature, wherein the size of a cuvette is as follows: the length is 1cm, the width is 1cm, and the height is 5 cm.

Preparation of reaction solution: respectively preparing 30L of each of 0.5mol/L calcium chloride and 0.5mol/L urea, and then mixing the calcium chloride and the urea with the same volume as 30L to obtain 60L of reaction liquid for later use.

A general method for preparing bentonite modified cement of each of the following experimental examples, comprising the steps of:

1) preparation of a modification solution: taking a specific OD₆₀₀225mL of the bacillus pasteurii suspension and 675mL of reaction liquid or water (used for different comparative experiments) are mixed uniformly to obtain a modified solution;

2) preparing bentonite cement: uniformly mixing the bentonite and ordinary portland cement according to a proportion to prepare cement (the total weight is 0.6KG) containing 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% of the bentonite, and simultaneously preparing 0.6KG of ordinary portland cement (namely, 0 wt% of the bentonite) and a sterile control group sample (the bacteria suspension and the reaction solution are not added, the same amount of water is added according to the same general method for comparison, and the proportions of the bentonite in the cement are respectively set to be 0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt%);

3) uniformly mixing the cement prepared in the step 2) and the modified solution prepared in the step 1).

Experimental example 1

Following the principles of parallel experiments, a cement containing 20 wt% bentonite was prepared according to the general procedure described above (20 wt% refers to the proportion in step 2, step 1 used 675mL of water instead of the reaction solution to make the modifying solution), with the difference between the groups being that the OD in step 1 was₆₀₀The intensities of 0 (i.e., pure water), 0.5, 1.0, 1.5 and 2.0, respectively, were measured in the above-described manner, and it is apparent that the bacterial concentration is OD, as shown in FIG. 1₆₀₀When the ratio is 1.0, no reaction liquid is added, so that the compression strength of the bentonite modified cement is greatly improved, and the cement has OD₆₀₀Compared with 0, the improvement is 32% at 28 days.

Experimental example 2

Following the principles of parallel experiments, a cement containing 20 wt% bentonite was prepared according to the general procedure described above (20 wt% refers to the ratio in step 2, step 1 used 675mL of reaction solution to make the modifying solution), with the difference between the groups being the OD in step 1₆₀₀0, 0.5, 1.0, 1.5 and 2.0, respectively, and the strength was measured as described above, and the results are shown in fig. 2. The experiment found that₆₀₀Comparing with 0:

as can be seen from FIG. 2, when the bacterial concentration is OD₆₀₀After 7 days and 28 days, the increase in compressive strength of the bentonite-modified cement (20% bentonite) by the bacterial suspension and the reaction solution was 90% and 80%, respectively, when the strain was 2.0. When the concentration of bacteria is OD₆₀₀The compressive strength increases were substantially the same for 1.0 and 1.5, with a yield increase of about 46% after 7 days and 59% after 28 days.

Experimental example 3

Following the principles of parallel experiments, bacteria-containing cements (OD in step 1) were prepared according to the general procedure described above₆₀₀675mL of the reaction solution prepared as 1), each group was distinguished in that the cement prepared in step 2 contained 0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 w% of bentonitet% and sterile control samples (no bacterial suspension and reaction solution added, but the same general method, the same amount of water added to control, the proportion of bentonite in cement is also set to 0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, respectively) were set, and the strength was measured according to the method described above, and the strength test for each sterile control sample is shown in FIG. 3a, and the results for the bacteria-containing cement are shown in FIG. 3 b. This experiment found that, compared to sterile control samples of the respective bentonite concentrations:

after mixing the bacterial suspension and the reaction solution in a cement cube (20% bentonite), the compressive strength increased by about 87.5% and 79% for 7 days and 28 days, respectively, compared to the control sample. After 7 and 28 days, the compressive strength of the cement (without bentonite) using the bacterial suspension and the reaction solution increased by 15% and 17%, respectively, compared to the control sample. After 10% bentonite was added to the cement, the bacterial suspension and the reaction solution increased the compressive strength by 14% and 20% over the control sample after 7 days and 28 days, respectively. After 30% bentonite was added to the cement, the bacterial suspension and the reaction solution increased the compressive strength by 136% and 78% over the control sample after 7 days and 28 days, respectively. Meanwhile, under the condition of bacterial suspension and reaction solution, the compressive strength of the cement (40% bentonite) is also better improved, the strength is improved by 163% after 7 days and 38% after 28 days.

Claims

1. A method for preparing bentonite modified cement, which comprises the step of mixing modified cement with a microbial inoculum, wherein the modified cement comprises bentonite and portland cement, and the microbial inoculum contains Bacillus pasteurianus.

2. The method as claimed in claim 1, wherein the modified cement is composed of sodium bentonite and ordinary portland cement, wherein the weight percentage of the sodium bentonite is 10% -40%; the volume mass ratio of the microbial inoculum to the modified cement is 1.5L: 1Kg, the pasteurella is pasteurella ATCC11859, and the using amount of the ATCC11859 bacteria is OD₆₀₀1/4 of the bacterial load in ATCC11859 bacterial solution of 1-2, OD was measured at room temperature with water as waterAnd (4) measuring by contrast.

3. The method of claim 2, wherein the OD of said aqueous solution of ATCC11859 bacteria is₆₀₀The weight percentage of the bentonite in the modified cement is 20 percent.

4. The method according to any preceding claim, wherein the microbial inoculum further comprises calcium ions and urea.

5. The method as claimed in claim 4, wherein the modified cement comprises 10-20%, 20-30% or 20-40% by weight of bentonite.

6. The method of claim 4, wherein the OD of said aqueous solution of ATCC11859 bacteria is₆₀₀Is 1-1.5 or 1.5-2.

7. The method of claim 4, wherein the calcium ions and urea are present in the same molar amount, e.g. in a concentration of 0.375 mol/L.

8. The method of claim 4, wherein the calcium ions are provided as calcium chloride.

9. The method according to any preceding claim, wherein the microbial inoculum is in the form of an aqueous solution.

10. A bentonite modified cement obtainable by the method of any preceding claim.