Method for determining panel concrete expansion agent content

Abstract

This invention discloses a method for determining the dosage of expansive agent in panel concrete. Based on the cement components that cause volume changes during the concrete setting and hardening process, the method eliminates the influence of sand and gravel components, which do not undergo volume changes during the process. By measuring the mass ratio of sand and gravel and cement to water in the panel concrete, and then calculating the concrete volume change rate for different expansive agent dosages using an expression, the corresponding expansive agent dosage is determined based on the volume change rate. This invention enables rapid determination of the expansive agent dosage for panel concrete with different mix proportions, overcoming the drawback of long experimental cycles in existing methods.

Description

Technical Field

[0001] This invention relates to the field of concrete preparation technology, and more specifically to a method for determining the admixture content of panel concrete. Background Technology

[0002] Concrete panels are widely used in water conservancy projects, serving to protect the main structure of the project and resist water seepage, and have an important impact on the safety and durability of the project structure.

[0003] Due to the large-area construction of concrete panels within a short period, the cumulative shrinkage deformation during the concrete's setting and hardening process can generate significant tensile stress along its length. When the length of the subsequently poured concrete panel is large (exceeding 100 meters) and simultaneously subjected to the restraining force of the previously poured concrete, the resulting tensile stress often exceeds the tensile strength of the concrete itself, leading to cracking and failure. Therefore, to prevent this failure, engineers add appropriate expansion agents to the concrete panel to counteract the volume shrinkage during the setting and hardening process, thus preventing cracking.

[0004] However, more expansive agent is not always better. Excessive expansive agent can cause bulging, warping, or even cracking of the concrete after offsetting shrinkage deformation, which can also harm the structural integrity. Therefore, determining the appropriate amount of expansive agent in panel concrete is crucial.

[0005] The current method for determining the dosage of expansive agent in concrete panels is through on-site experiments. Given a fixed concrete mix proportion, different dosages of expansive agent are added to prepare concrete panels. After 28 days of curing, the volume change rate of the concrete specimens is measured. The dosage of expansive agent that meets the requirements of the specification (GB / T 23439-2017 "Concrete Expansive Agent") is taken as the selected dosage. However, to meet construction requirements and mechanical properties, the concrete mix proportions often need to be continuously adjusted during the project. This means that the dosage of expansive agent must also be adjusted according to changes in the concrete mix proportions, resulting in a lengthy experimental cycle that can affect project progress.

[0006] The mechanism of volume shrinkage during the setting and hardening process of concrete is very clear: the volume change during the cement hydration reaction is the main cause of concrete volume shrinkage. The volume of the pre-hydration products is larger than the volume of the hydration products, thus causing shrinkage deformation. However, the sand and gravel in concrete do not participate in the hydration reaction during the setting and hardening process, and their volume remains unchanged before and after hydration. Meanwhile, when an expansive agent is added, the cement hydration products react further with the expansive agent, and the volume of the reaction products expands, offsetting the volume shrinkage caused by the hydration products, thereby inhibiting cracking of concrete due to shrinkage. The main components of cement, C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), and C4AF (tetracalcium aluminoferrite), all undergo hydration reactions, but the volume changes of the reactants before and after the reaction are different.

[0007] Based on the hydration reaction and the change in the volume of reactants before and after the reaction, the dosage of the expansion agent can be effectively determined by focusing on the content of the main components C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), and C4AF (tetracalcium aluminoferrite) in cement. Summary of the Invention

[0008] The purpose of this invention is to provide a method for determining the dosage of expansive agent in panel concrete. The determination process is based on the selected cement components, enabling rapid determination of the dosage of expansive agent in panel concrete with different mix proportions, thus overcoming the shortcomings of existing methods with long experimental cycles.

[0009] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0010] A method for determining the dosage of an expansion agent in panel concrete, the method comprising the following steps:

[0011] Step 1: Determine the content β of each component in cement: C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), and C4AF (tetracalcium aluminoferrite). C3S β C2S β C3A and β C4AF ;

[0012] Step 2: Mix C3S and water separately at a ratio of 2:1, and add expansion agent at mass percentages of 0%, 3%, 6%, 9%, 12%, and 15% of C3S. Cure for 28 days and measure the volume change rate V. C3S0 V C3S3 V C3S6 V C3S9 V C3S12 、 and V C3S15 ;

[0013] Step 3: Mix C2S and water separately at a ratio of 2:1, and add expansion agent at mass percentages of 0%, 3%, 6%, 9%, 12%, and 15% of C2S. Cure for 28 days and measure the volume change rate V. C2S0 V C2S2 V C2S4 V C2S6 V C2S8 、 and V C2S10 ;

[0014] Step 4: Mix C3A and water separately at a ratio of 2:1, and add 0%, 3%, 6%, 9%, 12%, and 15% (by mass) of C2S as an expansion agent. Cure for 28 days and measure the volume change rate V. C3A0 V C3A3 V C3A6 V C3A9 V C3A12 、 and V C3A15 ;

[0015] Step 5: Mix C4AF and water separately at a ratio of 2:1, and add 0%, 3%, 6%, 9%, 12%, and 15% (by mass) of expansion agent from C4AF. Cure for 28 days and measure the volume change rate V. C4AF0 V C4AF3 V C4AF6 V C4AF9 V C4AF12 、 and V C4AF15 ;

[0016] Step 6: Determine the mass ratio α of sand and gravel and (cement + water) in the panel concrete;

[0017] Step 7, according to the following expression

[0018]

[0019] The volume change rate Vi of concrete with different expansive agent dosages was calculated, where i = 0, 3, 6, 9, 12, and 15 represent expansive agent dosages of 0%, 3%, 6%, 9%, 12%, and 15%, respectively; the value range of i is 0-15%, which is a common expansive agent dosage in engineering.

[0020] Step 8: Based on the obtained Vi, find the volume change rate that is closest to the preset volume change rate V. REF The value V + and V - Given the corresponding expansion agent dosages m% and n%, the expansion agent dosage can be determined using the following formula:

[0021]

[0022] Furthermore, the curing temperature should not differ from the actual concrete placement temperature during construction by more than 5°C.

[0023] Furthermore, the mass ratio of the expanding agent added to C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), and C4AF (tetracalcium aluminoferrite) is between 0% and 15%. This range of the added expanding agent mass ratio is determined based on empirical values ​​accumulated in actual construction.

[0024] Furthermore, select 3-8 mass ratio values ​​between 0% and 15% for the expansion agent.

[0025] Furthermore, the mass ratio of the expansion agent added to C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), and C4AF (tetracalcium aluminoferrite) can be 0%, 2%, 4%, 6%, 8%, 10%, 12%, and 14%.

[0026] Furthermore, the preset volume change rate (VREF) is between 0.5‰ and 2.5‰. This preset volume change rate is determined according to GB / T23439-2017 "Concrete Expansion Agent".

[0027] Beneficial effects

[0028] (1) The method for determining the expansion agent is clear. Starting from the cement component that causes volume change during the concrete setting and hardening process, the influence of sand and gravel components that do not change volume during the concrete setting and hardening process is eliminated.

[0029] (2) The method for determining the amount of expansive agent is quick. Without changing the type of cement, the amount of expansive agent can be determined without additional experiments when changing the amount of concrete raw materials. This method is convenient and quick, and can improve experimental efficiency. Detailed Implementation

[0030] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments and experimental data.

[0031] Example 1:

[0032] The raw materials used are PO 42.5 ordinary Portland cement, C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), C4AF (tetracalcium aluminoferrite), calcium sulfoaluminate concrete expansion agent, sand (fineness modulus 2.7), and aggregate (particle size 5-20mm). The experimental temperature is 15-20℃. Determine the dosage of the concrete expansion agent to be added to the panel concrete according to the following steps:

[0033] Step 1: Determine the main components of the cement to be used based on the parameters provided by the cement manufacturer.

[0034] C3S: 52%; C2S: 17%; C3A: 10%; C4AF: 13%;

[0035] Step 2: Separately mix C3S and water in a 2:1 ratio, and add 0%, 3%, 6%, 9%, 12%, and 15% (by mass) of expansion agent from C3S. Mix in a mixer for 3 minutes to ensure uniform mixing. Pour the mixture into a 100mm × 100mm × 300mm mold and cure for 28 days. Measure the volume change rate V using a dial indicator. C3S0 V C3S3 V C3S6 V C3S9 V C3S12 、 and V C3S15 See Table 1;

[0036] Step 3: Mix C2S and water separately in a 2:1 ratio, and add 0%, 3%, 6%, 9%, 12%, and 15% (by mass) of expansion agent from C2S. Mix in a mixer for 3 minutes to ensure even mixing. Pour the mixture into a 100mm × 100mm × 300mm mold and cure for 28 days. Measure the volume change rate V using a dial indicator. C2S0 V C2S3 V C2S6 V C2S9 V C2S12 、 and V C2S15 See Table 1;

[0037] Step 4: Mix C3A and water separately in a 2:1 ratio, and add 0%, 3%, 6%, 9%, 12%, and 15% (by mass) of expansion agent from C3A. Mix in a mixer for 3 minutes to ensure even mixing. Pour the mixture into a 100mm × 100mm × 300mm mold and cure for 28 days. Measure the volume change rate V using a dial indicator. C3A0 V C3A3 V C3A6 V C3A9 V C3A12 、 and V C3A15 See Table 1;

[0038] Step 5: Mix C4AF and water separately in a 2:1 ratio, and add 0%, 3%, 6%, 9%, 12%, and 15% (by mass) of expansion agent from C4AF. Mix in a mixer for 3 minutes to ensure even mixing. Pour the mixture into a 100mm × 100mm × 300mm mold and cure for 28 days. Measure the volume change rate V using a dial indicator. C4AF0 V C4AF3 V C4AF6 V C4AF9 V C4AF12 、 and V C4AF15 See Table 1;

[0039] Step 6: Based on the selected concrete mix proportion (cement:water:sand:aggregate = 320:175:652:1320), determine the mass ratio of sand and aggregate to (cement + water) in the panel concrete as α = 4.0;

[0040] Step 7: Based on the following expression

[0041]

[0042] The concrete volume change rate Vi was calculated for different amounts of expansive agent (i = 0%, 3%, 6%, 9%, 12%, and 15%), as shown in Table 1.

[0043] Step 8: Select the preset volume change rate V based on engineering experience. REF =1.5‰, close to V obtained from Table 1 REF The value is 1.9‰ (V) + ) and 0.8‰ (V - The volume change rate formula is constructed based on the volumetric expansion agent dosages of 12% (m%) and 9% (n%), and then substituted into the formula:

[0044]

[0045] The calculated dosage of the expanding agent was determined to be 10.9%.

[0046] To demonstrate the effectiveness of this method in determining the dosage of expansive agent in panel concrete, a set of panel concrete specimens with the expansive agent dosage determined by this method were prepared. After 28 days of curing, the volume change rate was found to be 1.6‰, which is consistent with the preset volume change rate V. REF The result with a value of (1.5‰) has an error within 10%, which meets the engineering requirements. It can be seen that this method is superior to the traditional method for determining the dosage of expansive agent in panel concrete.

[0047] In practical engineering, the corresponding amount of expanding agent can be determined by using different preset volume change rates (e.g., between 0.5‰ and 2.5‰, meeting the specifications). When the preset volume change rate is V... REF When = 0.5‰, the value close to V obtained from Table 1 REF The value is 0.8 (V) + ) and -0.5 (V - The expansion agent dosages of 9% (m%) and 6% (n%) are used as the basis for calculation. Substituting these values ​​into the expansion agent dosage formula, the expansion agent dosage can be determined to be 8.3%. When a preset volume change rate of V is selected... REF When = 2.5‰, the value close to V obtained from Table 1 REF The value is 2.9 (V) + ) and 1.9 (V -The expansion agent dosage of 12% (m%) and 9% (n%) is calculated by substituting these values ​​into the expansion agent dosage formula, and the expansion agent dosage is determined to be 13.8%.

[0048] Table 1. Process for determining the dosage of expanding agent

[0049]

[0050]

[0051] Example 2:

[0052] The raw materials used are PO 42.5 ordinary Portland cement, C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), C4AF (tetracalcium aluminoferrite), calcium sulfoaluminate concrete expansion agent, sand (fineness modulus 2.7), and gravel (particle size 5-20mm), which are the same as those used in Case 1.

[0053] Because the cement used is the same as in Example 1, and steps 1 to 5 are the same as in Case 1, the volume change rate V C3S0 V C3S3 V C3S6 V C3S9 V C3S12 、 and V C3S15 V C2S0 V C2S3 V C2S6 V C2S9 V C2S12 、 and V C2S15 V C3A0 V C3A3 V C3A6 V C3A9 V C3A12 、 and V C3A15 V C4AF0 V C4AF3 V C4AF6 V C4AF9 V C4AF12 、 and V C4AF15 See Table 2;

[0054] Step 6: Based on the selected concrete mix proportion (cement:water:sand:stone = 295:175:667:1352), determine the mass ratio of sand and gravel to (cement + water) in the panel concrete as α = 4.3.

[0055] Step 7: Based on the expression as follows

[0056]

[0057] The concrete volume change rate Vi was calculated for different amounts of expansive agent (0%, 3%, 6%, 9%, 12%, and 15%), as shown in Table 2.

[0058] Step 8: Select the preset volume change rate V based on engineering experience. REF =1.5‰, close to V obtained from Table 2 REF The value is 1.8‰ (V) + ) and 0.8‰ (V - Substitute the values ​​of the expansion agent and their corresponding dosages of 12% (m%) and 9% (n%) into the formula:

[0059]

[0060] The calculated dosage of the expanding agent was determined to be 11.1%.

[0061] To demonstrate the effectiveness of this method in determining the dosage of expansive agent in panel concrete, a set of panel concrete specimens with the expansive agent dosage determined by this method were prepared. After 28 days of curing, the volume change rate was found to be 1.4‰, which is consistent with the preset volume change rate V. REF The result with a value of (1.5‰) has an error within 10%, which meets the engineering requirements. It can be seen that this method is superior to the traditional method for determining the dosage of expansive agent in panel concrete.

[0062] Table 2. Process for determining the dosage of expanding agent

[0063]

[0064]

[0065] Example 3:

[0066] The raw materials used are PO 42.5 ordinary Portland cement, C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), C4AF (tetracalcium aluminoferrite), calcium sulfoaluminate concrete expansion agent, sand (fineness modulus 2.7), and gravel (particle size 5-20mm). The raw materials are the same as in Example 1.

[0067] Because the cement used is the same as in Case 1, and steps 1 to 5 are the same as in Case 1, the volume change rate V C3S0 V C3S3 V C3S6 V C3S9 V C3S12 、 and V C3S15 V C2S0 V C2S3 V C2S6 V C2S9 V C2S12 、 and V C2S15 V C3A0V C3A3 V C3A6 V C3A9 V C3A12 、 and V C3A15 V C4AF0 V C4AF3 V C4AF6 V C4AF9 V C4AF12 、 and V C4AF15 See Table 3;

[0068] Step 6: Based on the selected concrete mix proportion (cement:water:sand:stone = 253:175:682:1378), determine the mass ratio of sand and gravel to (cement + water) in the panel concrete as α = 4.8.

[0069] Step 7: Based on the following expression

[0070]

[0071] The concrete volume change rate Vi was calculated for different amounts of expansive agent (0%, 3%, 6%, 9%, 12%, and 15%), as shown in Table 3.

[0072] Step 8: Select the preset volume change rate V based on engineering experience. REF =1.5‰, close to V obtained from Table 3 REF The value is 1.6‰ (V) + ) and 0.7‰ (V - Substitute the values ​​of the expansion agent and their corresponding dosages of 12% (m%) and 9% (n%) into the formula:

[0073]

[0074] The calculated dosage of the expanding agent was determined to be 11.7%.

[0075] To demonstrate the effectiveness of this method in determining the dosage of expansive agent in panel concrete, a set of panel concrete specimens with the expansive agent dosage determined by this method were prepared. After 28 days of curing, the volume change rate was found to be 1.6‰, which is consistent with the preset volume change rate V. REF The result with a value of (1.5‰) has an error within 10%, which meets the engineering requirements. It can be seen that this method is superior to the traditional method for determining the dosage of expansive agent in panel concrete.

[0076] Table 3. Process for determining the dosage of expanding agent

[0077]

[0078]

[0079] Based on the three cases above, it can be seen that the method for determining the expansion agent dosage of panel concrete proposed in this patent is quick and simple. When using the same raw materials to prepare panel concrete of different strength grades, only steps 1 to 5 need to be performed once, and then the appropriate dosage of expansion agent can be selected based on the data results. Based on engineering experience, the dosage of expansion agent in the range of 0-15% is selected, and the values ​​of 0%, 3%, 6%, 9%, 12%, and 15% are selected as experimental dosages. Five dosage experiments can reduce the experimental steps and time of traditional methods, improving experimental efficiency. At the same time, compared with the results of traditional methods, the method for determining the dosage of expansion agent proposed in this invention is reliable and convenient.

Claims

1. A method for determining the dosage of expansion agent in panel concrete, characterized in that, The method includes the following steps: Step 1: Determine the content β of each component in cement: C3S tricalcium silicate, C2S dicalcium silicate, C3A tricalcium aluminate, and C4AF tetracalcium aluminoferrite. C3S β C2S β C3A and β C4AF ; Step 2: Mix C3S and water separately at a ratio of 2:1, and add expansion agent at concentrations of 0%, 3%, 6%, 9%, 12%, and 15% of C3S by mass. Cure for 28 days and measure the volume change rate (V). C3S0 V C3S3 V C3S6 V C3S9 V C3S12 、 and V C3S15 ; Step 3: Mix C2S and water separately at a ratio of 2:1, and add expansion agents at mass percentages of 0%, 3%, 6%, 9%, 12%, and 15% of C2S. Cure for 28 days and measure the volume change rate (V). C2S0 V C2S3 V C2S6 V C2S9 V C2S12 、 and V C2S15 ; Step 4: Mix C3A and water separately at a ratio of 2:1, and add expansion agent at concentrations of 0%, 3%, 6%, 9%, 12%, and 15% of C3A by mass. Cure for 28 days and measure the volume change rate V. C3A0 V C3A3 V C3A6 V C3A9 V C3A12 、 and V C3A15 ; Step 5: Mix C4AF and water separately at a ratio of 2:1, and add 0%, 3%, 6%, 9%, 12%, and 15% (by mass) of expansion agent from C4AF. Cure for 28 days and measure the volume change rate V. C4AF0 V C4AF3 V C4AF6 V C4AF9 V C4AF12 、 and V C4AF15 ; Step Six: Determine the mass ratio α of sand, gravel, cement, and water in the concrete panel. Step 7: Based on the following expression ， Calculate the concrete volume change rate Vi for different expansive agent dosages, where i = 0, 3, 6, 9, 12, and 15 represent expansive agent dosages of 0%, 3%, 6%, 9%, 12%, and 15%, respectively. Step 8: Find the volume change rate V that is closest to the preset volume change rate based on the obtained Vi. REF The value V + and V - Given the corresponding expansion agent dosages m% and n%, the expansion agent dosage is determined by the following formula: ， Among them, the preset volume change rate V REF Between 0.5‰ and 2.5‰.

2. The method for determining the dosage of expansion agent in panel concrete according to claim 1, characterized in that, The curing temperature should not differ from the actual concrete placement temperature during construction by more than 5°C.

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