Mix proportion design method for mass concrete based on the heat of hydration of mineral admixtures

Abstract

The present invention discloses a mix proportion design method for mass concrete based on the hydration heat of mineral admixtures, which includes the following steps: S1. Taking the strength and adiabatic temperature rise of the target concrete as the mix proportion design indexes of the concrete, determine the types of mineral admixtures; S2. Calculate the water consumption and cement dosage C that meet the strength of the target concrete when using pure cement f ; S3. Calculate the cement dosage C that meets the target adiabatic temperature rise T of the concrete when using pure cement Q ; S4. Determine the strength activity K f and the hydration heat adjustment coefficient K Q ; S5. Calculate the dosage A of the mineral admixture and the cement dosage C; S6. Calculate the mix proportion of the target concrete. The present invention takes the adiabatic temperature rise of the mass concrete as the target performance to participate in the mix proportion calculation, reduces the hydration heat of the cementitious materials while meeting the strength of the concrete, and further reduces the shrinkage of the mass concrete caused by temperature

Description

Technical Field

[0001] The invention relates to the technical field of concrete mix design, and in particular to a large volume concrete mix design method based on hydration heat of mineral admixtures. Background Art

[0002] With the development of social economy and the deepening of urban construction, the form of buildings has become more complex and diversified, and the demand for large-volume concrete structures is growing. In addition, many engineering structures have closely combined large-volume concrete with high strength, low heat, and low shrinkage. Therefore, the performance requirements and preparation technology of large-volume concrete are becoming higher and higher. Large-volume concrete has disadvantages such as large hydration heat release and high shrinkage risk. The mix design needs to take into account both hydration heat and strength. At present, the concrete mix design methods used in engineering are mostly implemented in accordance with the requirements of JGJ55-2011 "Ordinary Concrete Mix Design Code", but this method is mainly a concrete mix design method with strength as the control index. For the hydration heat requirements of large-volume concrete, it is only proposed that the 3d and 7d hydration heat of cementitious materials should not be greater than 240kJ / kg and 270kJ / kg respectively, and the adiabatic temperature rise of concrete should not be greater than 50℃. The adiabatic temperature rise index of concrete and the hydration heat index of cementitious materials are not incorporated into the mix design.

[0003] Strength and hydration heat are two closely related indicators. Generally speaking, the higher the strength, the greater the hydration heat. How to coordinate the contradiction between strength and hydration heat and achieve the goal of large-volume concrete mix design taking into account low hydration heat and high strength is a question worth thinking about. The traditional mix design method fails to incorporate the hydration heat index of large-volume concrete into the mix design process, making it difficult to achieve the requirements of dual control of concrete strength and hydration heat. Summary of the invention

[0004] The purpose of the present invention is to provide a large-volume concrete mix design method based on the hydration heat of mineral admixtures, taking the adiabatic temperature rise of large-volume concrete as the target performance in the mix calculation, reducing the hydration heat of cementitious materials while meeting the concrete strength, thereby reducing the shrinkage of large-volume concrete caused by temperature.

[0005] The present invention is achieved through the following technical solutions:

[0006] The mass concrete mix design method based on the hydration heat of mineral admixtures includes the following steps:

[0007] S1. Take the target concrete strength and adiabatic temperature rise T as the concrete mix design index, determine the type of mineral admixture, and determine the type of cement and its corresponding total hydration heat Q based on the concrete strength index. C, determine the type of coarse aggregate and the type of water reducing agent;

[0008] S2. Based on the strength index and the selected coarse aggregate and water reducing agent, calculate the water consumption W and cement consumption C required to meet the target concrete strength when pure cement is used. f ;

[0009] S3, based on adiabatic temperature rise T, total hydration heat of cement Q C , and the specific heat capacity C of the target concrete p and density ρ, calculate the cement dosage C required to meet the target adiabatic temperature rise T of concrete when pure cement is used Q ;

[0010] S4. Determine the strength activity K of mineral admixtures f and hydration heat adjustment coefficient K Q ;

[0011] S5, based on the cement dosage C calculated in steps S2-S4 f , cement dosage C Q , strength activity K f and hydration heat adjustment coefficient K Q ; Calculate the amount of mineral admixture A and cement C;

[0012] S6. Calculate the target concrete mix ratio based on the water consumption W, cement consumption C and mineral admixture consumption A determined in steps S1-S5.

[0013] Mass concrete refers to large volumes of concrete with the smallest geometric dimension of the concrete structure not less than 1m, or concrete that is expected to cause harmful cracks due to temperature changes and shrinkage caused by hydration of cementitious materials in the concrete.

[0014] Concrete is composed of water, cement, mineral admixtures and water reducing agents, among which cement and mineral admixtures are cementitious materials. The existing large-volume concrete mix design takes into account the hydration heat of cementitious materials, resulting in the designed concrete formula not taking into account both low hydration heat and high strength, causing the concrete to shrink due to temperature.

[0015] This paper takes advantage of the different effects of different hydration activities of mineral admixtures on the strength and adiabatic temperature rise of concrete, and uses the activity value and hydration heat of the admixtures to equate the cementitious system with mineral admixtures to cement. Finally, a group of calculation equations for cementitious materials that simultaneously meet the requirements of strength and adiabatic temperature rise are obtained. The hydration heat, i.e., the adiabatic temperature rise index, is included in the mix design stage, so as to achieve the purpose of taking both hydration heat and strength into consideration in the mix design of large-volume concrete.

[0016] Furthermore, in step S2, the water consumption W and cement consumption C f The calculation process is as follows:

[0017] S21. Calculate the concrete mixing strength f based on the strength index of the target concrete cu,0 ;

[0018] S22. Based on the concrete mixing strength f obtained in step S21 cu,0 , combined with the regression coefficient corresponding to the coarse aggregate selected in step S1 and the 28-day mortar compressive strength of the cementitious material, calculate the water-binder ratio W / C f ,

[0019] S23. Based on the slump requirement of the target concrete, as well as the type of coarse aggregate and the water reduction rate β of the water reducer, calculate the water consumption W;

[0020] S24. Based on the water-binder ratio W / C obtained in step S22 f and the water consumption W obtained in step S23, calculate the cement dosage C f .

[0021] Furthermore, in step S21, the calculation formula for the concrete mixing strength f cu,0 is as follows:

[0022] f cu,0 = f cu,k + 1.645σ

[0023] In the formula, f cu.0 is the concrete strength mixing value, with the unit of MPa; f cu.k is the target concrete strength value, with the unit of MPa; σ is the standard deviation, with the unit of MPa.

[0024] Furthermore, in step S22, the calculation formula for the water-binder ratio W / C f is as follows:

[0025]

[0026] In the formula, W is the water consumption, with the unit of Kg; B is the cementitious material dosage, with the unit of Kg. When the cementitious material is only cement, the cementitious material dosage B is the cement dosage C f ; f cu.0 is the concrete strength mixing value, with the unit of MPa; α a , α b are both regression coefficients of the coarse aggregate; f b is the 28-day mortar compressive strength of the cementitious material, with the unit of MPa, which can be measured or calculated by multiplying the cement strength grade by the corresponding enrichment coefficient; when using pure cement, the calculation formula for f b is:

[0027] f b = λ ce f ce,g

[0028] Among them, λ c is the surplus coefficient of the cement strength grade value, and f ce,g is the cement strength grade value.

[0029] Furthermore, in step S23, the calculation formula for the water consumption W is as follows:

[0030] m wo = m wo' (1 - β)

[0031] In the formula, m wo represents the unit water consumption that meets the slump requirement when adding water-reducing agent, that is, the water consumption W, and β is the water reduction rate.

[0032] Furthermore, in step S3, the calculation formula for the cement dosage C Q is as follows:

[0033]

[0034] In the formula, C p is the specific heat capacity of concrete, with the unit of kJ / (kg·℃); ρ is the density of concrete, with the unit of kg / m 3 ; Q C is the total hydration heat Q C of cement, with the unit of kJ / kg; T is the adiabatic temperature rise of the target concrete, with the unit of ℃.

[0035] Furthermore, in step S4, the strength activity K f is calculated using the ratio of the 28-day strength data of the mortar with mineral admixture to the strength of the pure cement mortar of the same mass, and the hydration heat adjustment coefficient K Q is calculated using the ratio of the total hydration heat release of the mortar with mineral admixture to the total hydration heat release of the pure cement of the same mass.

[0036] For example: when the mineral admixture is fly ash, the relationship functions between the fly ash strength activity K f , the fly ash hydration heat adjustment coefficient K f and FA / C are established respectively, where FA is the fly ash dosage and C is the cement dosage. The fitted formula is:

[0037] K f = 0.99 - 0.44×FA / C, K Q = 0.90 - 0.62×FA / C.

[0038] Furthermore, in step S5, the calculation formulas for the mineral admixture dosage A and the cement dosage C are as follows:

[0039]

[0040] The cementitious material includes the cement and mineral admixtures. Calculate the dosage A of the mineral admixtures and the dosage C of the cement, which are the cementitious material dosages that simultaneously meet the requirements of the target concrete strength and the target adiabatic temperature rise. Here, the cement dosage C is the cement dosage that simultaneously meets the requirements of the target concrete strength and the target adiabatic temperature rise.

[0041] In the above equations, C and A are the cement dosage and the mineral admixture dosage that simultaneously meet the strength and the adiabatic temperature rise, and they are the unknowns to be obtained. C f 、C Q 、K f 、K Q Have been obtained through steps S2 - S4. The significance of the equations is as follows: Assume that the cement dosage required to meet the target strength with pure cement is C f , and the cement dosage required to meet the adiabatic temperature rise is C Q . The cementitious material dosage incorporating the mineral admixtures multiplied by the corresponding activity value is the equivalent cement dosage. By using the different activity values of the mineral admixtures for different properties of the concrete, the mineral admixtures are equivalent to cement, and finally, a system of equations for cement dosage balance is obtained.

[0042] When the mineral admixture is fly ash, substitute the K f and K Q obtained in step S4 into the system of equations to obtain the following system of equations.

[0043]

[0044] Furthermore, in step S6, on the basis of having determined the water dosage W, the cement dosage C, and the mineral admixture dosage A, determine the sand dosage and the stone dosage, and determine the dosage ratios of water, cement, mineral admixtures, sand (fine aggregate), and stone (coarse aggregate) in the target concrete.

[0045] Furthermore, in step S1, the mineral admixture includes at least one of fly ash, slag powder, and silica fume.

[0046] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0047] 1. The design method of the present invention takes the adiabatic temperature rise of mass concrete as the target performance to participate in the mix proportion calculation, reduces the hydration heat of the cementitious material while meeting the concrete strength, and further reduces the shrinkage of mass concrete caused by temperature.

[0048] 2. Through the design method of the present invention, concrete that simultaneously meets the strength and the adiabatic temperature rise can be designed. Specific Embodiments

[0049] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and do not limit the present invention.

[0050] Embodiment 1: A mix proportion design method for mass concrete based on the heat of hydration of mineral admixtures, comprising the following steps:

[0051] S1. Taking the strength and adiabatic temperature rise T of the target concrete as the mix proportion design indexes of the concrete, determining the type of mineral admixture, and determining the type of cement and its corresponding total heat of hydration Q based on the strength index of the concrete C , and determining the types of coarse aggregates and water reducers;

[0052] For example: For an extra-large volume floor slab structure, pumped mass concrete is used for pouring, and the strength grade is C40 mass concrete. Due to the huge volume of the concrete, there are clear requirements for the heat of hydration and adiabatic temperature rise of the concrete, that is, not exceeding 45°C. Therefore, in this embodiment, the concrete strength grade is taken as C40, the adiabatic temperature rise of the concrete is 45°C, fly ash is selected as the mineral admixture, and the slump is 200 mm, meeting the pumping requirements.

[0053] According to JGJ55-2011 "Code for Mix Proportion Design of Ordinary Concrete", since the designed strength grade of the concrete in this embodiment is C40, ordinary Portland cement P.O42.5R is selected, and the total heat of hydration is 381 kJ / kg. Considering the local raw materials for concrete preparation, crushed stone with a coarse aggregate diameter of 5 - 31.5 mm is selected, fly ash is Class F Grade I ash, and a polycarboxylate high-performance water reducer with a water reduction rate of 30% is used. The concrete slump is set at 200 mm according to the actual engineering requirements.

[0054] S2. Based on the strength index and the selected coarse aggregates and water reducer, calculate the water consumption W and cement consumption C that meet the strength of the target concrete when using pure cement f :

[0055] S21. Calculate the concrete mix design strength f obtained based on the strength index of the target concrete cu,0 ;

[0056] According to the formula in JGJ55-2011 "Code for Mix Proportion Design of Ordinary Concrete":

[0057] f cu,0 ≥f cu,k +1.645σ

[0058] In this embodiment, f cu,k is 40 MPa, the standard deviation is taken as 5 MPa, and the calculated concrete mix design strength f cu,0is 48 MPa, and the f of this embodiment cu,0 takes the minimum value. Therefore, the concrete mix design strength f cu,0 is calculated as follows:

[0059] f cu,0 = f cu,k + 1.645σ

[0060] In the formula, f cu.0 is the concrete strength mix value, with the unit of MPa; f cu.k is the concrete target strength value, with the unit of MPa; σ is the standard deviation, with the unit of MPa.

[0061] S22. Based on the concrete mix design strength f cu,0 obtained in step S21, combined with the regression coefficients corresponding to the coarse aggregate selected in step S1 and the 28-day mortar compressive strength of the cementitious material, calculate the water-binder ratio W / C f :

[0062] According to JGJ55-2011 "Code for Design of Ordinary Concrete Mix Proportions", the formula for obtaining the water-binder ratio W / C f is as follows:

[0063]

[0064] In the formula, W is the water consumption, with the unit of Kg; B is the cementitious material consumption, with the unit of Kg. When the cementitious material is only cement, the cementitious material consumption B is the cement consumption C f ; f cu.0 is the concrete strength mix value, with the unit of MPa; α a , α b are both regression coefficients of the coarse aggregate; f b is the 28-day mortar compressive strength of the cementitious material, with the unit of MPa.

[0065] In the above formula, f cu,0 is 48 MPa. When the coarse aggregate is crushed stone, the regression coefficients α a , α b take 0.53 and 0.2 respectively. f b is the 28-day mortar compressive strength of the cementitious material. According to JGJ55-2011 "Code for Design of Ordinary Concrete Mix Proportions", the calculation formula is:

[0066] f b = γ f γ s f ce ; f ce = γ c f ce,g

[0067] When using pure cement, γf and γ c both take 1. γ c is the richness coefficient, which takes 1.16 in this embodiment. f ce,g is the cement strength grade. The cement strength grade is 42.5 in this embodiment. It can be calculated that f b = 42.5×1.16 = 49.3 MPa. Substituting the above into the water-binder ratio calculation formula, we have

[0068]

[0069] S23. Based on the slump requirement of the target concrete, the type of coarse aggregate, and the water reduction rate β of the water reducer, calculate and obtain the water consumption W:

[0070] The determination of the water consumption W is related to the slump of the concrete, the variety and size of the coarse aggregate, and the water reduction rate β of the admixture. According to the formula m wo = m wo' (1-β) in the "Code for Design of Mix Proportions of Ordinary Concrete" JGJ55-2011. When the slump requirement of the concrete is 200 mm, the value of m wo' is 230 kg, and β is the water reduction rate of the water reducer, taking 28%. It is calculated that m wo is 166 kg. In the formula, m wo represents the unit water consumption that meets the slump requirement when adding the water reducer, that is, the water consumption W = 166 kg in this embodiment.

[0071] S24. Based on the water-binder ratio W / C f obtained in step S22 and the water consumption W obtained in step S23, calculate and obtain the cement consumption C f :

[0072] The cement consumption that meets the strength when using pure cement is:

[0073] C f = 166 / 0.49 = 339 kg.

[0074] S3. Based on the adiabatic temperature rise T, the total heat of hydration Q C of the cement, and the specific heat capacity C p and density ρ of the target concrete, calculate the cement consumption C Q that meets the target adiabatic temperature rise T of the concrete when using pure cement:

[0075] The calculation formula for the cement consumption C Q is as follows:

[0076]

[0077] In the formula, C pis the specific heat capacity of concrete, with the unit of kJ / (kg·℃); ρ is the density of concrete, with the unit of kg / m 3 ; Q C is the total hydration heat Q C of cement, with the unit of kJ / kg; T is the adiabatic temperature rise of the target concrete, with the unit of ℃.

[0078] The density of concrete is taken as 2400 kg / m 3 , the specific heat capacity is taken as 0.97 kJ / (kg·℃), substituting the target adiabatic temperature rise value T = 45℃ and the total hydration heat release of cement Q C = 381 kJ / kg into the formula for calculation, we get:

[0079]

[0080] At this time, the cement dosage C f to meet the target strength is 339 kg, and the cement dosage C Q to meet the target adiabatic temperature rise is 275 kg.

[0081] S4. Determine the strength activity K f and the hydration heat adjustment coefficient K Q of mineral admixtures:

[0082] Calculate the strength activity K f using the ratio of the 28-day strength data of mortar with mineral admixtures to the strength of pure cement mortar of the same mass, and calculate the hydration heat adjustment coefficient K Q using the ratio of the total hydration heat release of mortar with mineral admixtures to the total hydration heat release of pure cement of the same mass:

[0083] When the mineral admixture is fly ash, establish the relationship functions of the fly ash strength activity K f and the fly ash hydration heat adjustment coefficient K f with FA / C respectively, where FA is the fly ash dosage and C is the cement dosage. The fitted formula is:

[0084] K f = 0.99 - 0.44×FA / C, K Q = 0.90 - 0.62×FA / C.

[0085] S5. Based on the cement dosages C f , C Q , the strength activity K f and the hydration heat adjustment coefficient K Q obtained from steps S2 - S4; calculate the mineral admixture dosage A and the cement dosage C:

[0086] The calculation formulas for the mineral admixture dosage A and the cement dosage C are as follows:

[0087]

[0088] When the mineral admixture is fly ash, the calculation formulas for the dosage A of the mineral admixture and the dosage C of cement are as follows:

[0089]

[0090] Substitute C f = 339 kg and C Q = 275 kg into the system of equations, and solve the system of binary quadratic equations to obtain C = 300 kg and FA = 110 kg.

[0091] S6. Based on the water consumption W, cement dosage C, and mineral admixture dosage A determined in steps S1 - S5, calculate the target concrete mix proportion:

[0092] According to the water consumption W = 166 kg, cement dosage C = 300 kg, and fly ash dosage FA = 110 kg obtained in the above steps, the water - binder ratio W / C = 166 / (300 + 110)=0.40. Determine the sand ratio β s = 0.42; According to the mass method, the unit weight of concrete is 2400 kg / m 3 , then the dosage of sand is m s =(2400 - 166 - 300 - 110)×0.42 = 766 kg, and the dosage of gravel is m g =(2420 - 161 - 296 - 110)×0.58 = 1058 kg. The final concrete mix proportion that simultaneously meets the 28 - day compressive strength of 40 MPa and the adiabatic temperature rise not exceeding 45°C is: water consumption W is 166 kg, cement dosage C is 300 kg, fly ash dosage FA is 110 kg, sand dosage is 766 kg, and gravel dosage is 1058 kg.

[0093] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A mix proportion design method for mass concrete based on the hydration heat of mineral admixtures, characterized in that It includes the following steps: S1. Take the strength and adiabatic temperature rise T of the target concrete as the design indexes for the concrete mix proportion, determine the types of mineral admixtures, and determine the type of cement and its corresponding total heat of hydration Q based on the strength index of the concrete C , and determine the types of coarse aggregates and water reducers; S2. Calculate the water consumption W and cement consumption C that meet the target concrete strength when using pure cement based on the strength index, selected coarse aggregate and water reducer. f ; S3. Based on the adiabatic temperature rise T, the total heat of hydration Q of cement C , and the specific heat capacity C of the target concrete p and density ρ, calculate the cement dosage C that meets the target adiabatic temperature rise T of the concrete when using pure cement Q ; S4. Determine the strength activity K of mineral admixtures f and the hydration heat adjustment coefficient K Q ; S5. The cement dosage C obtained based on the calculations in steps S2 - S4 f , the cement dosage C Q , the strength activity K f and the heat of hydration adjustment coefficient K Q ; calculate the amount A of mineral admixture and the cement dosage C; S6. Calculate the target concrete mix proportion based on the water consumption W, cement consumption C, and mineral admixture consumption A determined in steps S1 - S5; in step S2, the calculation processes of the water consumption W and the cement consumption C f are as follows: S21. Calculate the concrete mix design strength f based on the strength index of the target concrete cu,0 ; S22. Based on the concrete mixing strength f obtained in step S21 cu,0 , combined with the regression coefficient corresponding to the coarse aggregate selected in step S1 and the 28-day mortar compressive strength of the cementitious material, calculate the water-binder ratio W / C f , S23. Based on the slump requirement of the target concrete, as well as the type of coarse aggregate and the water reduction rate β of the water reducer, calculate and obtain the water consumption W; S24. Calculate the cement dosage C based on the water-cement ratio W / C obtained in step S22 f and the water consumption W obtained in step S23 f .

2. The mix proportion design method for mass concrete based on the hydration heat of mineral admixtures according to claim 1, characterized in that, In step S21, the calculation formula for the concrete mix design strength f cu,0 is as follows: f cu,0 = f cu,k + 1.645σ where f cu.0 is the prepared value of concrete strength, with the unit of MPa; f cu.k is the target strength value of concrete, with the unit of MPa; σ is the standard deviation, with the unit of MPa.

3. The mix proportion design method of mass concrete based on the hydration heat of mineral admixtures according to claim 1, characterized in that, In step S22, the water-cement ratio W / C f is calculated as follows: Where, W is the water consumption, in Kg; B is the amount of cementitious materials, in Kg. When the cementitious materials are only cement, the amount of cementitious materials B is the amount of cement C f ; f cu.0 is the configured value of concrete strength, in MPa; α a , α b are both regression coefficients of coarse aggregates; f b is the compressive strength of cement mortar of cementitious materials at 28d, in MPa.

4. The mix proportion design method of mass concrete based on the hydration heat of mineral admixtures according to claim 1, wherein, In step S23, the calculation formula for the water consumption W is as follows: m wo = m wo' (1 - β) where m wo represents the unit water consumption that meets the slump requirement when adding water reducing agent, i.e., water consumption W, and β is the water reduction rate.

5. The method for designing the mix proportion of mass concrete based on the heat of hydration of mineral admixtures according to claim 1, characterized in that In step S3, the cement dosage C Q is calculated as follows: Where C p is the specific heat capacity of concrete, with the unit of kJ / (kg·℃); ρ is the density of concrete, with the unit of kg / m 3 ; Q C is the total hydration heat Q C of cement, with the unit of kJ / kg; T is the adiabatic temperature rise of the target concrete, with the unit of ℃.

6. The mix proportion design method for mass concrete based on the heat of hydration of mineral admixtures according to claim 1, characterized in that, In step S4, the strength activity K is calculated using the ratio of the 28-day strength data of the mortar incorporated with mineral admixtures to the strength of the pure cement mortar of the same mass. f The heat of hydration adjustment coefficient K is calculated using the ratio of the total heat of hydration released by the mortar incorporated with mineral admixtures to the total heat of hydration released by the pure cement of the same mass. Q .

7. The mix proportion design method of mass concrete based on the hydration heat of mineral admixtures according to claim 1, characterized in that, In step S5, the calculation formulas for the amount A of mineral admixture and the amount C of cement are as follows:

8. The mix proportion design method of mass concrete based on the hydration heat of mineral admixtures according to claim 1, characterized in that, In step S6, on the basis of having determined the water consumption W, the amount C of cement and the amount A of mineral admixture, determine the amount of sand and the amount of gravel, and determine the dosage ratio of water, cement, mineral admixture, sand and gravel in the target concrete.

9. The mix proportion design method for mass concrete based on the hydration heat of mineral admixtures according to any one of claims 1-8, characterized in that In step S1, the mineral admixture includes at least one of fly ash, slag powder and silica fume.

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