A design method for the mix proportion of cementitious sand-gravel material

Abstract

The present invention discloses a method for designing the mix proportion of cementitious sand and gravel materials, which includes obtaining the required preparation strength of the cementitious sand and gravel materials through calculation; using the rock materials excavated at the construction site for jaw crushing to obtain jaw-crushed coarse aggregates; selecting different sieve hole sizes according to the preparation strength, and setting the ideal grading passing rate range according to the calculation formula of the ideal grading passing rate of the coarse aggregates, determining the aggregate particle sizes to be added to the jaw-crushed coarse aggregates, and forming the final coarse aggregate mixed grading; selecting different sieve hole sizes according to the preparation strength, and selecting the mixing optimization target according to the engineering characteristics to form the final fine aggregate grading, and selecting the main cementitious materials according to the preparation strength. This method for designing the mix proportion of cementitious sand and gravel materials can optimize the proportion of the coarse aggregates and the fine aggregates, thereby obtaining high-quality coarse aggregates and fine aggregates, and further improving the quality of the cementitious sand and gravel materials (CSG), enabling the project to proceed smoothly.

Description

Technical Field

[0001] The present invention relates to the field of building materials, and particularly to a method for designing the mix proportion of cementitious sand-gravel materials. Background Art

[0002] Cementitious sand-gravel material (CSG) is a low-cost and low-strength building material proposed on the basis of concrete research. The basic components of CSG and conventional concrete both include coarse aggregate, fine aggregate, cementitious material, water, and chemical additives, etc. The ideal filling and wrapping theory of concrete can be summarized as follows: (1) The coarse aggregate, i.e., gravel, is wrapped by the sand-containing cementitious paste, and the voids of the coarse aggregate are exactly filled by the mortar; (2) The fine aggregate, i.e., sand, is wrapped by the cementitious neat paste, and the voids of the fine aggregate are exactly filled by the neat paste. Therefore, the core of optimizing the aggregate gradation and mix proportion design lies in making the mixture reach the maximum density and the cementitious paste just fill the voids of the aggregate, so as to improve the quality of the cementitious sand-gravel material (CSG).

[0003] However, at the field construction site, due to the influence of conditions such as engineering environment, materials, and construction period, how to optimize and obtain high-quality coarse aggregate and fine aggregate has always been an important factor restricting the cementitious sand-gravel material (CSG). Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the technical problem to be solved by the present invention is to provide a method for designing the mix proportion of cementitious sand-gravel materials, which can optimize the ratio of coarse aggregate and fine aggregate, thereby obtaining high-quality coarse aggregate and fine aggregate, and further improving the quality of the cementitious sand-gravel material (CSG) to ensure the smooth progress of the project.

[0005] To achieve the above object, the present invention is realized by the following technical solutions: A method for designing the mix proportion of cementitious sand-gravel materials, comprising:

[0006] By calculation, obtain the required mixing strength of the cementitious sand-gravel material;

[0007] Use the rock material excavated at the construction site for jaw crushing processing to obtain jaw-crushed coarse aggregate with a particle size of 19.0 - 300 mm, and screen and grade the jaw-crushed coarse aggregate according to the particle size;

[0008] Design and optimization method for the mix proportion of coarse aggregate: According to the mixing strength, select different sieve hole sizes, and set the ideal gradation passing rate range according to the ideal gradation passing rate calculation formula for coarse aggregate. According to the ideal gradation passing rate range, determine the aggregate particle size to be added to the jaw-crushed coarse aggregate to make the particulate aggregate gradation tend to be optimal and form the final coarse aggregate mixed gradation;

[0009] Design and optimization method for fine aggregate mix proportion: According to the mixing strength, different sieve pore sizes are selected, and the mixing optimization target is selected according to the engineering characteristics. The artificially crushed sand and natural ultra-fine river sand are screened according to the mixing optimization target, and the proportion calculation analysis and mixing optimization are carried out to form the final fine aggregate gradation; and

[0010] Design of gel materials: According to the mixing strength, the main gel materials are selected.

[0011] Furthermore, the calculation formula for the mixing strength is as follows:

[0012] f cu,o =f cu,k +t·σ

[0013] In the formula, f cu,o is the CSG mixing strength (MPa), f cu,k is the strength standard value at the CSG design age (MPa), t is the probability coefficient, generally 0.84 is selected for temporary structures when the guarantee rate is 80%, and σ is the standard deviation of the CSG compressive strength (MPa).

[0014] Furthermore, the calculation formula for the passing rate of the ideal gradation of coarse aggregates (Fuller formula) is:

[0015]

[0016] In the formula, P is the cumulative passing percentage through the sieve with aperture d, d is the sieve aperture (mm), D is the nominal maximum aggregate size (mm), and x is a constant (0.5 for pebbles and 0.8 for crushed stones).

[0017] Furthermore, the method for determining the final mixed gradation of coarse aggregates is:

[0018] According to the calculated ideal gradation value, set the ideal gradation passing rate interval;

[0019] Mix and optimize the jaw-crushed coarse aggregates of 19.0 - 300 mm and other aggregates with different particle sizes of 4.75 - 19.0 mm according to different weight percentages to form various mixed gradations of coarse aggregates, select the mixed gradation of coarse aggregates within the ideal gradation passing rate interval, and finally obtain the optimized mixing ratio value of the jaw-crushed coarse aggregates of 19.0 - 300 mm and the coarse aggregates of 4.75 - 19.0 mm.

[0020] Furthermore, the mixing optimization target is the sand gradation interval in Zone III.

[0021] Further, according to the sand gradation range of Zone III, artificial sand with a fineness modulus of 2.65 and natural river sand are mixed in different proportions, and the fineness modulus of the mixed sand after mixing is 1.91, forming various fine aggregate mixed gradations. The fine aggregate mixed gradation within the sand gradation range of Zone III is selected to obtain the final optimized mixing ratio value of the coarse aggregate.

[0022] Further, the gelling material further includes a water reducing agent, a setting retarder, and a mineral admixture.

[0023] Further, the mineral admixture is local volcanic ash.

[0024] Advantages of the present invention:

[0025] The above-mentioned design method for the mix proportion of gelled gravel materials first performs jaw crushing on the excavated rock, realizing the jaw crushing treatment and recycling of the excavated stone materials. After gradation analysis and mixing optimization, aggregates suitable for CSG mixing are formed, which can not only improve the quality of gelled gravel materials (CSG), solve the problem of local material shortage, but also reduce the environmental impact of excavated waste materials. Description of the drawings

[0026] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for the specific embodiments will be briefly introduced below. In all the drawings, the components or parts do not necessarily draw according to the actual proportion.

[0027] Figure 1 It is a schematic diagram of the coarse aggregate mixed gradation curve in a design method for the mix proportion of gelled gravel materials provided by an embodiment of the present invention;

[0028] Figure 2 For Figure 1 shown is a schematic diagram of the fine aggregate mixed gradation curve in a design method for the mix proportion of gelled gravel materials; Specific embodiments

[0029] The embodiments of the technical solutions of the present invention will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0030] Please refer to Figures 1 to 2 , the present invention provides a design method for the mix proportion of gelled gravel materials, including the following steps:

[0031] S110. Through calculation, obtain the required preparation strength of the gelled gravel materials;

[0032] S120. Use the rock materials excavated at the construction site for jaw crushing to obtain jaw-crushed coarse aggregates with a particle size of 19.0 - 300 mm, and screen and classify the jaw-crushed coarse aggregates according to the particle size.

[0033] S130. Design and optimization method for the mix proportion of coarse aggregates: According to the required compressive strength, select different sieve hole sizes, and set the passing rate range of the ideal gradation according to the calculation formula for the passing rate of the ideal gradation of coarse aggregates. According to the passing rate range of the ideal gradation, determine the aggregate particle sizes to be added to the jaw-crushed coarse aggregates to make the particle aggregate gradation tend to be optimal and form the final coarse aggregate mixed gradation.

[0034] S140. Design and optimization method for the mix proportion of fine aggregates: According to the required compressive strength, select different sieve hole sizes, and select the mixing optimization target according to the project characteristics. Screen the artificial crushed sand and natural ultra-fine river sand according to the mixing optimization target, and conduct proportion calculation analysis and mixing optimization to form the final fine aggregate gradation; and

[0035] S150. Design of gel materials: Select the main gelling materials according to the required compressive strength.

[0036] By using this mix proportion design method for cementitious gravel materials, the jaw crushing treatment and recycling of the excavated stone materials are realized. After gradation analysis and mixing optimization, aggregates suitable for CSG mixing are formed, which can not only improve the quality of cementitious gravel materials (CSG), but also solve the problem of local material shortage and reduce the environmental impact of excavation waste.

[0037] In specific implementation, the required CSG mixing strength can be calculated and determined according to the "Technical Guidelines for Building Dams with Cemented Granular Materials" (SL 678-2014) in combination with the project requirements. The calculation method is shown in the following formula:

[0038] f cu,o =f cu,k +t·σ

[0039] In the formula, f cu,o is the CSG mixing strength (MPa), f cu,k is the strength standard value at the CSG design age (MPa), t is the probability coefficient, generally select the value of 0.84 when the guarantee rate is 80% for temporary structures, and σ is the standard deviation of the CSG compressive strength (MPa).

[0040] Taking the manufacture of the Nyerere Hydropower Station in Tanzania as an example: The design requirement for the cofferdam strength of the Nyerere Hydropower Station is that the cube compressive strength of concrete in 90 days is not less than 5 MPa. Referring to the standard "Code for Design of Mix Proportion of Ordinary Concrete" (JG J55-2011) and "Technical Guidelines for Building Dams with Cemented Granular Materials" (SL 678-2014), taking the standard deviation σ value as 4 MPa, the required mixing strength of CSG is obtained, as shown in Table 1. Based on the particularity of CSG and the characteristics of the temporary structure of the water-retaining cofferdam itself, the maximum size of coarse aggregate is mainly below 300 mm.

[0041] Table 1

[0042]

[0043] CSG Design Strength Parameters of the Cofferdam of the Nyerere Dam Project

[0044] Based on the above calculations, after obtaining the required mixing strength of CSG for the project, the design and optimization of the coarse aggregate mix proportion of CSG and the design and optimization of the fine aggregate mix proportion are carried out, and experimental verification is carried out.

[0045] In this embodiment, the calculation formula for the passing rate of the ideal gradation of coarse aggregate (Fuller formula) is:

[0046]

[0047] In the formula, P is the cumulative passing percentage through the sieve with aperture d, d is the aperture of the sieve (mm), D is the maximum nominal aggregate size (mm), and x is a constant (0.5 for pebbles and 0.8 for crushed stones).

[0048] And the method for the final mixed gradation of coarse aggregate is:

[0049] 1. Set the ideal gradation passing rate interval according to the calculated ideal gradation value;

[0050] 2. Optimize the mixing of the jaw-crushed coarse aggregate of 19.0 - 300 mm and other aggregates with different particle sizes of 4.75 - 19.0 mm according to different weight percentages to form various mixed gradations of coarse aggregate, select the mixed gradation of coarse aggregate within the ideal gradation passing rate interval, and finally obtain the optimized mixing ratio value of the jaw-crushed coarse aggregate of 19.0 - 300 mm and the coarse aggregate of 4.75 - 19.0 mm.

[0051] Taking the design of the cemented sand and gravel material obtained at the Nyerere Hydropower Station as an example:

[0052] For different sieve hole sizes between 4.75 - 300 mm, calculate the ideal gradation values and set the ideal gradation passing rate intervals. Optimize the mixing of jaw-crushed coarse aggregates of 19.0 - 300 mm and other aggregates of different particle sizes from 4.75 - 19.0 mm according to different weight percentages to form various coarse aggregate mixed gradations. Select the coarse aggregate mixed gradations within the ideal gradation passing rate intervals and form a coarse aggregate mixed gradation curve, such as Figure 1 。

[0053] From Figure 1 it can be seen that the single-particle-size coarse aggregate gradation of the jaw crusher does not meet the requirements of the ideal gradation interval of the Fuller formula and cannot be directly used. The overall mixed gradation curve is within the ideal gradation interval, meeting the requirements of the dense packing theory. At this time, the voids between the mixed coarse aggregates are small, and the mixing density and homogeneity are good.

[0054] Subsequently, according to the above theoretical gradation results, determine the mass mixing ratio of 0.85:0.15 for the jaw-crushed material with a single particle size of 19.0 - 300 mm and the aggregate with a single particle size of 4.75 - 19.0 mm as the optimized mixing ratio value of the coarse aggregate, and form the calculated ideal gradation of the coarse aggregate as shown in Table 2:

[0055] Table 2

[0056]

[0057] Single-particle-size coarse aggregate gradation and mixed gradation

[0058] In this embodiment, the mixing optimization target is selected as the sand gradation interval in Zone III.

[0059] The specific selection method is as follows:

[0060] A large amount of natural ultra-fine river sand has silted up at the bend of the upper reaches of the project riverbed. According to the regulations of the national standard "Sand for Construction" (GB / T 14684-2022), the fineness of sand is divided into 4 grades according to the fineness modulus: (I) Coarse sand with a fineness modulus of 3.7 - 3.1 and an average particle size of more than 0.5 mm; (II) Medium sand with a fineness modulus of 3.0 - 2.3 and an average particle size of 0.5 - 0.35 mm; (III) Fine sand with a fineness modulus of 2.2 - 1.6 and an average particle size of 0.35 - 0.25 mm; (IV) Extra-fine sand with a fineness modulus of 1.5 - 0.7 and an average particle size of less than 0.25 mm.

[0061] The fineness modulus calculation formula is:

[0062] M x =(A 2.36 +A 1.18 +A 0.6 +A 0.3 +A 0.15 -5·A4.75 ) / (100 - A 4.75 )

[0063] Wherein, A 0.15 represents the cumulative percentage of residue on the sieve of particles with a particle size of 0.15 mm (%), and so on for the others.

[0064] In the "Quality Standard and Test Method for Sands Used in Ordinary Concrete" (JGJ 52-92), it is stipulated that for sands with different gradations, the applicable ranges are also different: Sands in Zone Ⅰ belong to the coarse sand range and are not suitable for preparing building materials with less cementitious materials, as it is easy to increase the sand content rate. Sands in Zone Ⅱ are composed of medium sands and a part of relatively coarse fine sands and are suitable for preparing concrete and mortar. Sands in Zone Ⅲ are composed of fine sands and a part of relatively fine medium sands, and their characteristics are relatively large viscosity, good water retention, and a reduced sand content rate.

[0065] The gradation of the locally available natural river sand is shown in Table 3, and its fineness modulus is measured to be 1.42, with the composition being too fine and not meeting the requirements of the gradation zone. To simultaneously meet the workability requirements of CSG, reduce the unit water consumption, and make better use of local resources, the natural ultra-fine river sand is mixed and optimized with a small amount of artificially crushed sand to increase the content of coarse sand and raise the fineness modulus to the allowable range. Considering the actual characteristics of the temporary project of the water-retaining cofferdam, Zone Ⅲ sand is selected as the target for mixing optimization (other gradations of sand materials in different zones can be selected according to the actual project requirements), and the gradation range of Zone Ⅲ sand is shown in Table 3.

[0066] Subsequently, according to the gradation range of Zone Ⅲ sand, artificial sand with a fineness modulus of 2.65 is mixed with natural river sand in different proportions, and the fineness modulus of the mixed sand after mixing is 1.91, forming various fine aggregate mixed gradations. The fine aggregate mixed gradation within the gradation range of the said Zone Ⅲ sand is selected to obtain the final optimized mixing ratio.

[0067] Still taking the design of the cementitious gravel and sand materials of the Nyerere Hydropower Station as an example:

[0068] For different sieve hole sizes, first select the gradation of Zone Ⅲ sand as the target for mixing optimization, and this mixing optimization target is shown in Table 3. Subsequently, according to the gradation range of the said Zone Ⅲ sand, artificial sand with a fineness modulus of 2.65 is mixed with natural river sand in different proportions, and the fineness modulus of the mixed sand after mixing is 1.91, and various fine aggregate mixed gradations are formed. The fine aggregate mixed gradation within the gradation range of Zone Ⅲ sand is selected, and a fine aggregate mixed gradation curve is formed as Figure 2 .

[0069] Subsequently, according to the above theoretical gradation results, the mass mixing ratio of mixing artificial sand with a fineness modulus of 2.65 and natural river sand in different proportions for single particle size is determined, and the finally optimized coarse aggregate optimization mixing ratio value is 6:4, and an ideal calculated gradation of coarse aggregate is formed as shown in Table 3:

[0070] Table 3

[0071]

[0072] Gradation of artificial crushed sand, natural ultra-fine river sand and their mixed gradation

[0073] In this embodiment, the main cementitious material is the CEM II / B-L42.5N type cement produced by the local Twiga Cement Factory in Tanzania. Considering the location of the project area, transportation conditions and production costs, a water reducing agent is used in the gel material to reduce the unit cement consumption and improve the workability of CSG.

[0074] In this embodiment, the CEM II / B-L42.5N type cement produced by the local Twiga Cement Factory in Tanzania can be selected as the main cementitious material.

[0075] Furthermore, the gel material also includes a water reducing agent, a retarder and mineral admixtures.

[0076] Specifically, considering the remote location of the project area and difficult transportation, in order to save costs, a water reducing agent is used in the project to reduce the unit cement consumption and improve the workability of CSG. Considering that the CSG mixture should have strong fluidity in the project construction design method, a retarder is selected during the mixing process to meet the project construction requirements. At the same time, according to the local conditions and engineering experience, combined with the engineering economy and environmental protection needs, local volcanic ash is selected to replace fly ash as a mineral admixture in the construction. On the basis of ensuring the strength requirements, the replacement of cement materials is realized, and the production cost of CSG is reduced.

[0077] The cementitious gravel material obtained by using this design method of the cementitious gravel material mix ratio ensures its workability and compactness. The innovative practice realizes the jaw crushing treatment and utilization of the excavated stone materials, solves the problem of shortage of natural materials in the project area, and reduces the environmental impact of the excavated waste materials. In addition, by changing the volcanic ash content of the cementitious material, a trial mix ratio test of CSG materials is carried out. According to the test results and engineering requirements, when the volcanic ash content is 58.3%, the designed mix ratio of CSG materials can meet the engineering construction requirements and is controllable and stable, while achieving the maximum economy. The designed mix ratio of this CSG material has been successfully applied to the actual construction of the overflow cofferdam of the Julius Nyerere Hydropower Station. The proposed design method of the CSG mix ratio based on jaw crushed materials not only provides an economical and reasonable solution for the design of CSG materials for the overflow cofferdam of the Julius Nyerere Hydropower Station, but also provides reference for the mix ratio design of building materials under such complex conditions during the construction of other projects.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. A design method for the mix proportion of cementitious sand-gravel material, characterized in that, Including: Through calculation, the required mixing strength of the cementitious gravel material is obtained; The rock material excavated at the construction site is processed by jaw crushing to obtain jaw-crushed coarse aggregates with a particle size of 19.0 - 300 mm, and the jaw-crushed coarse aggregates are screened and graded according to the particle size; Design and optimization method for the coarse aggregate mix ratio: According to the mixing strength, different sieve hole sizes are selected, and according to the calculation formula for the passing rate of the ideal gradation of coarse aggregates, an ideal gradation passing rate range is set. According to the ideal gradation passing rate range, the aggregate particle sizes to be added to the jaw-crushed coarse aggregates are determined to make the particulate aggregate gradation tend to be optimal and form the final coarse aggregate mixed gradation; Among them, the method for determining the final coarse aggregate mixed gradation is: According to the calculated ideal gradation value, an ideal gradation passing rate range is set; the jaw-crushed coarse aggregates of 19.0 - 300 mm and other aggregates of different particle sizes of 4.75 - 19.0 mm are mixed and optimized according to different weight percentages to form various coarse aggregate mixed gradations. The coarse aggregate mixed gradation within the ideal gradation passing rate range is selected, and finally the optimized mixing ratio value of the jaw-crushed coarse aggregates of 19.0 - 300 mm and the coarse aggregates of 4.75 - 19.0 mm is obtained; Design and optimization method for the fine aggregate mix ratio: According to the mixing strength, different sieve hole sizes are selected, and according to the engineering characteristics, a mixing and optimization target is selected. The artificial crushed sand and natural ultra-fine river sand are screened according to the mixing and optimization target, and ratio calculation analysis and mixing optimization are carried out to form the final fine aggregate gradation; Among them, the mixing and optimization target is the sand gradation range in Zone III; and according to the sand gradation range in Zone III, the artificial sand with a fineness modulus of 2.65 and natural river sand are mixed in different proportions to obtain a mixed sand fineness modulus of 1.91 after mixing, forming various fine aggregate mixed gradations. The fine aggregate mixed gradation within the sand gradation range in Zone III is selected to obtain the final optimized mixing ratio value of the coarse aggregates; Design of the gel material: According to the mixing strength, the main gel material is selected.

2. The design method of the mix proportion of the cementitious sand-gravel material according to claim 1, characterized in that The calculation formula for the mixing strength is: Wherein, f cu,o is the CSG preparation strength (MPa), f cu,k is the strength standard value at the CSG design age (MPa), t is the probability coefficient. For temporary structures, the value of 0.84 corresponding to a guarantee rate of 80% is generally selected, is the standard deviation of the CSG compressive strength (MPa).

3. The design method of the mix proportion of the cemented sand-gravel material according to claim 1, characterized in that, The calculation formula for the passing rate of the ideal gradation of the coarse aggregates (Fuller formula) is: In the formula, P is the cumulative passing percentage through the sieve with aperture d, d is the aperture of the sieve (mm), D is the nominal maximum size of the aggregate (mm), x is a constant (0.5 for pebbles and 0.8 for crushed stones).

4. The design method of the mix proportion of the cementitious sand-gravel material according to claim 1, characterized in that The gel material also includes water reducer, retarder and mineral admixture.

5. The design method of the mix proportion of the cementitious gravel material according to claim 4, characterized in that The mineral admixture is the locally available volcanic ash.

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