CN104310895A - Method for determining stable MgO doped amount of hydraulic concrete in sand simulation way - Google Patents

Abstract

The invention discloses a method for determining the stable content of MgO in hydraulic concrete by means of sand simulation. When the present invention determines the stable dosage of MgO in hydraulic concrete, the coarse aggregate (i.e. stone) in the concrete is replaced with sand of equal quality, and MgO is added to the concrete according to a conventional method to make concrete specimens; the concrete Measure the initial length L _s of the specimen after curing and constant temperature treatment; then measure the length L _f of the concrete specimen after boiling, pressure steaming, cooling and constant temperature treatment, and divide the difference between L _f and L _s by the test The effective length of the specimen is 250mm to obtain the autoclave expansion rate of the specimen; then, the obtained autoclave expansion rate of the concrete specimens with different MgO content is plotted as a curve of the autoclave expansion rate with the MgO content, in order The MgO content corresponding to the inflection point with the largest curvature on the curve is used as the stable MgO content of the corresponding hydraulic concrete. The invention can scientifically and rationally further increase the stable MgO content of the hydraulic concrete.

Description

The Method of Determining the Stable Dosage of MgO in Hydraulic Concrete by Sand Simulation

technical field

The invention relates to a method for determining the stable content of MgO in hydraulic concrete by adopting a sand simulation method, and belongs to the technical field of hydraulic and hydropower engineering concrete.

technical background

The external MgO concrete mixed with a certain amount of special magnesium oxide (MgO) in the hydraulic concrete has good delayed micro-expansion characteristics. Utilizing this feature can significantly improve the crack resistance of hydraulic concrete, simplify the construction of concrete retaining dam projects, shorten the construction period of water conservancy and hydropower projects, and save project investment. At present, the method used to determine the stability of MgO in hydraulic concrete is to refer to "Test Method for Cement Pressure Steam Stability (GB/T750-1992)" (hereinafter referred to as "GB/T750-1992"). That is: the mixing and forming of the cement paste test piece shall be carried out completely in accordance with GB/T750-1992; the cement mortar test piece shall be mixed according to the actual mixing ratio, and the mortar test piece shall be used instead of the cement paste test piece for pressure steaming test, and the rest shall be in accordance with GB/T750-1992; when mixing concrete specimens, use the actual mix ratio of the project, and then deduct the coarse aggregate in the concrete mix ratio, that is, keep the lime-sand ratio unchanged, and the rest of the operating process is also in accordance with GB/T750-1992 conduct. The size of the test pieces is 25mm×25 mm×280mm. The formed test pieces are cured, steamed and calculated according to the provisions of GB/T750-1992, and the steam expansion rate is 0.5%. The dosage of MgO is a stable dosage. The amount of MgO determined according to this traditional method is relatively small, and the amount of MgO is generally 3% to 5% based on the percentage of the total amount of cementitious materials (cement + fly ash). After being mixed into concrete, it cannot fully reach The amount of expansion required by the design. In order to solve this problem, the Chinese patent document application number is 201210328969.2, and the title of the invention is "a method for determining the stable content of MgO in hydraulic concrete", which discloses a technical solution of "stone powder simulation method". When mixing the autoclaved specimens, adopt the mix ratio of concrete to be used in the actual project, replace the coarse and fine aggregates in the concrete with the same amount of stone powder, that is, use stone powder, cement, and water to mix together, and form the autoclaved specimens (the size is 25mm×25mm×280mm), then, according to the provisions of GB/T 750-1992, curing, autoclaving and calculating the autoclave expansion rate, the corresponding MgO content when the autoclave expansion rate of the test piece is 0.5% is used as the concrete The stable dosage of MgO in the medium. Although the stable MgO content determined by the "stone powder simulation method" is higher than that of the existing method, it still cannot fully meet the expansion required by the design. Therefore, the existing method for determining the stable content of MgO in hydraulic concrete is still not ideal and needs further improvement.

Contents of the invention

The purpose of the present invention is to provide a method for determining the stable MgO content in hydraulic concrete by using a sand simulation method that can further increase the stable content of MgO and better meet the expansion required by engineering design, so as to overcome the current situation. There is a lack of access technology.

Technical scheme of the present invention is realized like this:

A method of using sand simulation to determine the stability of MgO in hydraulic concrete is as follows: determine the stability of MgO in hydraulic concrete mixed with cement, admixture, sand aggregate, water and other raw materials. When adding the amount, the concrete mix ratio to be used in the actual project is used to prepare the concrete specimen, but the coarse aggregate (ie stone) in the concrete needs to be replaced by sand of the same quality, and MgO is added to the concrete according to the conventional method, and then passed Adjust the amount of high-efficiency water reducer for concrete to obtain a mixture with the same consistency as cement slurry, and then make concrete specimens with reference to the national standard GB/T750-1992; after the concrete specimens are formed, combine the formed concrete specimens with Place the formwork together in a standard curing room with a temperature of 20±2°C and a relative humidity greater than 95% for curing for 48 hours; then remove the formwork of the specimen, and place the concrete specimen after removal of the formwork in a constant temperature room at 20±2°C for 1 hour After ~2h, measure the initial length L of the test piece _{the s} Then put the concrete specimen into the boiling box and boil for 3 hours. After the water temperature drops to room temperature, take out the concrete specimen and put it in a constant temperature room at 20±2°C for 12±3h; Put the test piece into the autoclave for autoclaving, the autoclave conditions are pressure 2.0±0.05MPa, temperature 215.7±1.3℃, constant pressure autoclave time is 3h; autoclaving is completed and the pressure in the autoclave drops to 0.1MPa Discharge the steam in the autoclave, and when the temperature in the autoclave drops to room temperature 20±2°C, take out the test piece and put it in a constant temperature room at 20±2°C for 12±3 hours, then measure its length L _f , with L _f with L _{the s} The difference is divided by the effective length 250mm of the test piece to get the steam expansion rate of the test piece; the pressure steam expansion rate of the test piece with different MgO content can be obtained by the above method; the obtained concrete test piece with different MgO content The autoclave expansion rate of the parts is drawn as a curve of the autoclave expansion rate versus the MgO content, and the MgO content corresponding to the inflection point with the largest curvature on the curve is used as the MgO stable content of the corresponding hydraulic concrete.

The above-mentioned sand is the sand used in corresponding projects, and the fineness modulus of the sand should be 2.2-2.8.

The size of the above formed concrete specimen is 25mm×25mm×280mm.

The above-mentioned MgO is MgO specially used for hydraulic concrete, and the firing temperature of the MgO is 1050°C to 1150°C.

Due to the adoption of the above-mentioned technical scheme, under the same existing conditions, the present invention uses the simulated composition of concrete coarse aggregate (i.e. replaces stones with sand) in the autoclaved test piece produced by the "sand simulation method", so that The amount of MgO contained in the unit volume of the test piece is less than the existing current method, so the pressure steam expansion rate of the test piece measured by the "sand simulation method" is obviously lower than the value measured by the existing current method, which is different from the actual engineering The deformation test results of concrete mixed with MgO are closer. That is to say, it is more reasonable to use the test results of the "sand simulation method" to evaluate the stability of the externally added MgO concrete than the current current method. Tests have proved that the stable MgO content of the concrete determined by the present invention is about 1-2 percentage points higher than that of the "stone powder simulation method".

Therefore, compared with the existing prevailing technology, the present invention can not only further increase the stable MgO content of hydraulic concrete and better meet the requirements of engineering design for hydraulic concrete expansion, but also is easy to operate and intuitive to judge.

Description of drawings

Fig. 1 is the comparative graph of the pressure steam expansion rate of the test piece with the change of MgO content by adopting the present invention and adopting "stone powder simulation method" to determine the stable content of MgO of hydraulic concrete.

Detailed ways

Below, the present invention will be further described in conjunction with examples.

Example of the present invention: when implementing a kind of sand simulation mode of the present invention to determine the method of MgO stable dosage in hydraulic concrete, the raw materials and the mix ratio that its concrete specimen adopts are all the same as the prior art, and the used MgO MgO is specially used for hydraulic concrete, and its firing temperature is 1050 ° C ~ 1150 ° C; when determining the stable MgO content of hydraulic concrete mixed with cement, admixture, sand and gravel aggregate, water and other raw materials, use The concrete mix ratio to be used in the actual project is used to prepare concrete specimens, but the coarse aggregate (ie stone) in the concrete needs to be replaced by sand of equal quality (the sand used is the sand used in the corresponding project, and its fineness modulus should be controlled at 2.2 to 2.8), and then add MgO to the concrete according to the conventional method, and then adjust the amount of high-efficiency water reducer for concrete to obtain a mixture with the same consistency as cement slurry, and then carry out concrete according to the national standard GB/T750-1992 Specimen production, the size of the formed concrete specimen is 25mm×25mm×280mm; after the concrete specimen is formed, place the specimen together with the formwork in a standard curing room with a temperature of 20±2°C and a relative humidity greater than 95%. Medium curing for 48h; then remove the formwork of the concrete specimen, put the specimen after removal of the formwork in a constant temperature room at 20±2°C for 1h to 2h, measure the initial length L of the test specimen _{the s} Then put the concrete specimen into the boiling box and boil for 3 hours. After the water temperature drops to room temperature, take out the concrete specimen and put it in a constant temperature room at 20±2°C for 12±3h; The test piece is placed in an autoclave for autoclave, and the autoclaving conditions are pressure 2.0±0.05MPa, temperature 215.7±1.3°C, and constant pressure autoclave time for 3h; Discharge the steam in the autoclave after it is below MPa, and when the temperature in the autoclave drops to room temperature 20±2°C, take out the test piece and put it in a constant temperature room at 20±2°C for 12±3h, then measure its length L _f , with L _f with L _{the s} The difference is divided by the effective length 250mm of the test piece to get the steam expansion rate of the test piece; the pressure steam expansion rate of the test piece with different MgO content can be obtained by the above method; the obtained concrete test piece with different MgO content The autoclave expansion rate of the parts is drawn as a curve of the autoclave expansion rate versus the MgO content, and the MgO content corresponding to the inflection point with the largest curvature on the curve is the MgO stable content of the corresponding hydraulic concrete.

Below is the example that adopts the present invention and adopts " stone powder simulation method " to determine the MgO stable dosage of hydraulic concrete to compare: mix ratio is P.O 42.5 cement consumption 275Kg/m ³ , sand consumption 850 Kg/m ³ , small stone dosage 510Kg/m ³ , The dosage of Chinese stone is 765Kg/m ³ , water consumption 151.25 Kg/m ³ For the prepared C30 hydraulic concrete, if the "stone powder simulation method" with application number 201210328969.2 is used to determine the stable MgO content of hydraulic concrete, it is necessary to first grind sand and gravel into stone powder with the same or similar fineness as the cement used, and then According to the total weight of the original sand and gravel 2125Kg/m ³ Weigh the stone powder according to its proportion, then stir it with cement and water according to the regulations of GB/T750-1992, make cement-stone powder pressure steamed test piece and carry out the pressure steam test, and the MgO corresponding to the steam expansion rate of 0.5% The dosage is used as the stable dosage of MgO in the corresponding hydraulic concrete, which is 5.8% at this time (see "Stone Powder Simulation Method Curve" in Figure 1). However, when adopting the present invention to make pressure steamed test pieces, it is not necessary to grind sand and stones into stone powder. It directly utilizes sand and other qualities to replace small stones and medium stones, that is, according to the total weight of the original sand and stones 2125Kg/m ³ Weigh the sand according to its proportion, and then mix it with cement, water and other raw materials according to the provisions of GB/T750-1992, make cement-sand pressure steamed test pieces and conduct pressure steaming tests, and use the pressure steaming expansion rate with the MgO content change curve The amount of MgO corresponding to the obvious inflection point of is used as the stable amount of MgO in the corresponding hydraulic concrete. In this example, the MgO content corresponding to the inflection point with the largest curvature on the curve of the autoclave expansion rate varied with MgO content is 7.5% (see "sand simulation method curve" in accompanying drawing 1), the The value is 1.7 percentage points higher than that of the "Stone Dust Simulation Method". Therefore, by adopting the present invention, the stable MgO content of hydraulic concrete can be further increased scientifically and rationally, so as to better meet the engineering design requirement for hydraulic concrete expansion.

Claims (4)

1. A kind of method that adopts sand simulation mode to determine the stable dosage of MgO in hydraulic concrete, it is characterized in that: in determining the hydraulic concrete that is mixed by raw materials such as cement, admixture, sandstone aggregate, water When the MgO content is stable, the concrete mix ratio to be used in the actual project is used to prepare the concrete specimen, but the coarse aggregate (ie stone) in the concrete needs to be replaced by sand of the same quality, and MgO is added to the concrete according to the conventional method. Then adjust the amount of high-efficiency water reducer for concrete to obtain a mixture with the same consistency as cement slurry, and then make concrete specimens with reference to the national standard GB/T750-1992; after the concrete specimens are formed, the formed concrete specimens Place the specimen together with the formwork in a standard curing room with a temperature of 20±2°C and a relative humidity greater than 95% for curing for 48 hours; then remove the formwork of the specimen, and place the concrete specimen after removal of the formwork into a constant temperature chamber at 20±2°C After leaving it aside for 1h-2h, measure the initial length L _s of the test piece; then put the concrete test piece into the boiling tank and boil for 3h. After the water temperature drops to room temperature, take out the concrete test piece and put it in the Put it aside in a constant temperature room at ±2°C for 12±3h; then put the test piece into an autoclave for autoclave, the autoclave conditions are pressure 2.0±0.05MPa, temperature 215.7±1.3°C, constant pressure autoclave time 3h; After the autoclave is completed and the pressure in the autoclave drops below 0.1MPa, the steam in the autoclave is discharged. When the temperature in the autoclave drops to room temperature 20±2°C, take out the test piece and put it in a constant temperature room at 20±2°C for 12 After ±3h, measure its length L _f , divide the difference between L _f and L _s by the effective length of the test piece 250mm to get the pressure steam expansion rate of the test piece; through the above method, test pieces with different MgO content can be obtained The autoclaved expansion rate of the obtained concrete specimens with different MgO content is plotted as a curve of the autoclaved expansion rate with the MgO content, and the MgO content corresponding to the inflection point with the largest curvature on the curve is The amount is used as the stable dosage of MgO in the corresponding hydraulic concrete. 2. The method for determining the stable dosage of MgO in hydraulic concrete by means of sand simulation according to claim 1, characterized in that: the above-mentioned sand is sand used in corresponding projects, and the fineness modulus of the sand should be 2.2 to 2.8 . 3. The method for determining the stable dosage of MgO in hydraulic concrete by sand simulation according to claim 1, characterized in that: the size of the formed concrete test piece is 25mm×25mm×280mm. 4. The method for determining the stable dosage of MgO in hydraulic concrete by means of sand simulation according to claim 1, characterized in that: the MgO is special MgO for hydraulic concrete, and the firing temperature of the MgO is 1050° C. 1150°C.