Patent ID: 12227460

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical scheme in the embodiments of the present invention will be described more clearly and completely hereinafter with reference to the accompanying drawings, apparently, the described embodiments are only some but not all of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without involving any creative effort shall fall within the scope of protection of the present disclosure.

In order to make the objective, characteristics solution, and advantages of the present invention more obvious and easier to understand, the present invention will be further described in detail below with reference to accompanying drawings and detailed embodiments.

The raw materials in the embodiment of the present invention are obtained by purchasing from commercially available means;

wherein the mechanical properties of PE fiber are shown in Table 1:

TABLE 1DiameterLengthStrengthElastic moduleDensity(μm)(mm)(MPa)(GPa)(g/cm3)241830001160.97

The physical and chemical properties of S105 slag, class F fly ash, and silica fume are shown in Table 2:

TABLE 2S105Class FSilicaslagfly ashfumewt %CaO344.01/SiO234.553.9794.73Al2O317.731.15/SO31.642.20.2Fe2O31.034.16/MgO6.011.01/TiO2/1.13/Others5.122.375.07LOI(%)0.844.61.5density (g/cm3)3.12.32.25D10(μm)1.653.550.10D50(μm)8.6814.460.14D90(μm)24.0958.880.35

The ultra-high molecular weight polyethylene fiber is a fiber spun from polyethylene with a molecular weight of 1 million-5 million in the embodiment of the present invention.

The sodium silicate is purchased from Jiashan Yourui Refractory Co., Ltd., model SP50 in the embodiment of the present invention.

The low speed refers to the stirring rate of 75 r/min, and the high speed refers to the stirring rate of 165 r/min in the embodiment of the present invention.

Embodiment 1

a low carbon ultra-high performance engineered geopolymer composite, comprising the following parts by weight of raw materials:cementitious material powder (S105 slag 821.1 parts, class F fly ash 248.9 parts, silica fume 93 parts) 1163 parts, fine aggregate (fine sand and medium sand are 346.0 parts and 61.1 parts, respectively, and the fine sand particle size is 40-200 μm, medium sand particle size is 200-700 m) 407.1 parts, admixture (barium chloride 0.01 parts, defoamer 0.001 parts, sodium lignosulfonate 0.005 parts) 18.6 parts, nano calcium carbonate (particle size 10-100 nm) 23.3 parts, reinforcing fiber (ultra-high molecular weight polyethylene fiber) 19.4 parts;wherein, 932.2 parts of activator and 81.6 parts of water are also comprised;the NaOH—Na2SiO3activator is used as a basic activator, and Na2CO3is used as a supplementary activator to form a low carbon composite activator;the mass ratio of an equivalent Na2O in the activator to the cementitious material powder is 7%;

the mass ratio of the total mass of the solvent and water in the activator to a mass of the cementitious material powder is 0.3.

As shown inFIG.3, a preparation method for a low carbon ultra-high performance engineered geopolymer composite comprises the following steps:(1) firstly, the prepared and cooled to room temperature NaOH solution with a concentration of 14 mol/L is mixed with Na2SiO3solution, the modulus of the solution is adjusted to 1.35, and the activator is obtained after the solution is cooled, wherein the mass ratio of sodium hydroxide solution, sodium silicate solution, and sodium carbonate solution is 111.5:354.6:0.0;(2) the cementitious material powder is added to a stirrer and dry mixed at a low speed of 75 r/min for 3 min, then the quartz sand is added to the stirrer and dry mixed at a low speed of 75 r/min for 3 min, then the activator is mixed with water and is added to the stirrer to stir at a low speed for 1 min, then the machine is stopped and the water reducer and nano calcium carbonate are added to continue to stir at a high speed of 165 r/min for 2 min, then replaced with a low speed and all PE fibers are added within 3 min, finally, the fibers are dispersed uniformly under stirring at a low speed of 75 r/min for 2 min to obtain a slurry;(3) the slurry obtained in step (2) is poured into the mold to form, and placed on the vibration table to expel bubbles and flatten the surface of the specimen, then the specimen is covered with a water-retaining film and maintained in the laboratory environment for Id, and then the specimen is demoulded and maintained in water at room temperature for 28 d, to obtain a dumbbell-shaped concrete specimen, and its size is shown inFIG.2.

Embodiment 2

a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that the amount of activator added is 475.9 parts and the amount of water added is 65.6 parts.

The preparation method for a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that in step (1), after the solution is cooled, then 0.75Na2O % in 25% mass fraction of sodium carbonate solution is added, wherein, the mass ratio of sodium hydroxide solution, sodium silicate solution and sodium carbonate solution is 99.7:316.7:59.5.

Embodiment 3

a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that the amount of activator added is 485.4 parts and the amount of water added is 49.7 parts.

The preparation method for a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that in step (1), after the solution is cooled, then 1.5Na2O % in 25% mass fraction of sodium carbonate solution is added, wherein, the mass ratio of sodium hydroxide solution, sodium silicate solution and sodium carbonate solution is 87.6:278.7:119.1.

Embodiment 4

a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that the amount of activator added is 487.2 parts and the amount of water added is 70.7 parts.

The preparation method for a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that in step (1), the modulus of the solution is adjusted to 1.50, wherein, the mass ratio of sodium hydroxide solution, sodium silicate solution, and sodium carbonate solution is 93.2:394.0:0.0.

Embodiment 5

a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that the amount of activator added is 508.1 parts and the amount of water added is 59.8 parts.

The preparation method for a low carbon ultra-high performance engineered geopolymer composite is different from embodiment 1 in that in step (1), the modulus of the solution is adjusted to 1.65, wherein, the mass ratio of sodium hydroxide solution, sodium silicate solution, and sodium carbonate solution is 74.6:433.5:0.0.

Comparative Embodiment 1

a preparation method for a low carbon ultra-high performance engineered geopolymer is different from embodiment 1 in that in step (2), the addition order of nano calcium carbonate is changed, which comprises the following steps:

(2) the cementitious material powder is added to a stirrer and dry mixed at a low speed of 75 r/min for 3 min, then the quartz sand and nano calcium carbonate are added to the stirrer and dry mixed at a low speed of 75 r/min for 3 min, then the activator is mixed with water and is added to the stirrer to stir at a low speed for 1 min, then the machine is stopped and the water reducer is added to continue to stir at a high speed of 165 r/min for 2 min, then replaced with a low speed and all PE fibers are added within 3 min, finally, the fibers are dispersed uniformly under stirring at a low speed of 75 r/min for 2 min to obtain a slurry.

Comparative Embodiment 2

a preparation method for a low carbon ultra-high performance engineered geopolymer is different from embodiment 1 in that in step (2), the addition order of nano calcium carbonate is changed, which comprises the following steps:

(2) the cementitious material powder is added to a stirrer and dry mixed at a low speed of 75 r/min for 3 min, then the quartz sand is added to the stirrer and dry mixed at a low speed of 75 r/min for 3 min, then the activator is mixed with water and is added to the stirrer to stir at a low speed for 1 min, then the machine is stopped and the water reducer is added to continue to stir at a high speed of 165 r/min for 2 min, then replaced with a low speed and all PE fibers and nano calcium carbonate are added within 3 min, finally, the fibers are dispersed uniformly under stirring at a low speed for 2 min to obtain a slurry.

Technical Effect

1. Setting time:

FIG.4is the setting time of the slurry obtained in step (2) of embodiments 1-5. It can be seen fromFIG.4that the initial setting time and final setting time of geopolymer slurry increase with the increase of Na2CO3substitution. When the Na2CO3substitution is 1.5Na2O %, the initial setting time and final setting time of embodiment 3 are 47 min and 57 min, respectively, which are 56.7% and 42.5% higher than that of embodiment 1, respectively, this may be due to the replacement of Na2CO3with Na2SiO3, which reduces the pH value of the geopolymer liquid phase, delays the dissolution of Ca, Si, Al and other elements in the cementitious material powder, and the reduction of [SiO4]4−also delays the formation of three-dimensional network cementitious structure. In addition, it can be seen fromFIG.5that increasing the modulus of the activator solution can also effectively delay the condensation of the slurry. The initial setting time and final setting time of embodiment 5 with a solution modulus of 1.65 reached 57 min and 65 min, respectively. However, although the increase of the solution modulus prolonged the initial setting time, the time interval between the final setting and the initial setting is reduced, this may be due to the fact that although increasing the modulus is as effective as using Na2CO3to reduce the pH value of the geopolymer liquid phase, thereby delaying the initial setting. However, due to the increase of [SiO4]4−content, the dissolved cations are rapidly combined to form a three-dimensional network cementitious precipitate, which reduces the time interval between the initial setting and the final setting. The setting time of comparative embodiment 1 and comparative embodiment 2 is the same as that of embodiment 1, and the addition order of nano calcium carbonate has no effect on the setting time.

2. Compression test

The compression test is carried out according to ASTM C109/C109M (2020), the compression is loaded by force controlled, and the loading speed is at a rate of 1.75 kN/s.

FIG.5shows the compressive strength of UHP-EGC with different Na2CO3substitution and different activator modulus. The Si/Al and Ca/(Si+Al) in the invention are 2.27-2.46 and 0.34-0.36, respectively, and the compressive strength reaches more than 120 MPa. It is worth noting that a certain amount of Na2CO3substitution reduced the alkalinity of the activator, but increased the compressive strength of UHP-EGC (from 122.9 MPa to 126.7 MPa). This is mainly because the cluster structure formed by a certain amount of sodium carbonate substitution optimizes the particle size distribution of fresh geopolymer slurry, improves the compactness of geopolymer slurry, and thus improves the compressive strength. Similarly, it can be seen fromFIG.5that with the increase of the modulus of the activator, the compressive strength of UHP-EGC decreases, which is also caused by the decrease of the density of fresh geopolymer slurry caused by the increase of the modulus of the activator. The compressive strength of the comparative embodiment 1 and comparative embodiment 2 is reduced by 10 MPa and 5 MPa respectively compared with the embodiment 1, and the addition order of nano calcium carbonate has a significant effect on the compressive strength.

3. Tensile test

The tensile test is carried out according to JC/T2461 (2018), two linear variable differential transformers (LVDTs) are arranged on both sides of the specimen through the fixture to obtain the deformation in the measurement area of the tensile specimen, the tensile test uses the displacement control method to load at a speed of 0.5 mm/min.

(1)FIG.6shows the average change of crack width of UHP-EGC under different Na2CO3substitution and different activator modulus. With the increase of Na2CO3substitution, the crack width of UHP-EGC decreases first and then increases under the same tensile strain. In the tensile process, the maximum average crack width of embodiment 2 is only 65.78 μm, which is much lower than that of the other two groups. This indicates that a certain amount of Na2CO3substitution helps to reduce the crack width. However, when the amount of Na2CO3substitution increases to 1.5Na2O %, the average crack width of UHP-EGC (embodiment 3) increases, which is about 100 m to 120 m. This indicates that excessive Na2CO3substitution will reduce the crack control capability of UHP-EGC. With the increase of the modulus of the activator, the average crack width of UHP-EGC exceeds 100 m. In particular, the average crack width of embodiment 4 reached 185.68 μm in the limit state. It can be seen that it is not conducive to the control of crack width under the condition of high activator modulus. The crack width of comparative embodiment 1 and comparative embodiment 2 increased by 12% and 7% respectively compared with that of embodiment 1, the addition order of nano calcium carbonate significantly effected the fiber-matrix interface performance, reduced the crack control capability, and increased the crack width.

(2)FIG.7shows the tensile stress-strain curves of UHP-EGC under different Na2CO3substitution and different activator modulus. It can be seen fromFIG.7that the change of Na2CO3substitution amount and activator modulus has a significant effect on the stress fluctuation, initial crack strength, tensile strength, and ultimate tensile strain of UHP-EGC during the strain hardening stage. It can be seen fromFIG.7that in the strain hardening stage, UHP-EGC has the behavior of stress fluctuation, the stress fluctuation is mainly caused by the stress redistribution process that the continuous initiation and stable development of UHP-EGC cracks with the increase of tensile deformation. For UHP-EGC with different Na2CO3substitutions, the stress fluctuation amplitude of the strain hardening state in embodiment 2 is the smallest, it can be seen that the fiber bridging effect is the best when the crack is initiated in embodiment 2 under tensile load, which is consistent with the observed minimum average crack width in embodiment 2. Increasing the modulus of the activator has the opposite effect on the stress fluctuation and crack control capability during the tensile strain hardening process of UHP-EGC.

(3)FIG.8shows the initial crack strength, tensile strength, ultimate tensile strain, and tensile strain energy of UHP-EGC under different Na2CO3substitution and different activator modulus. It can be seen from part a inFIG.8that the addition of Na2CO3significantly reduced the initial crack strength of UHP-EGC. The initial crack strength of embodiment 3 is 3.17 MPa, which is 31.7% lower than that of embodiment 1. On the contrary, in the Modulus Series, the initial crack strength increases with the increase of modulus. Especially when the modulus is 1.65, the initial crack strength of embodiment 5 is 5.92 MPa, which is 27.6% higher than that of embodiment 1. According to ECC design criteria, complementary energy (J′b) higher than matrix fracture energy (Jtip) is one of the prerequisites for ECC to have the capability of steady-state cracking, and the larger the pseudo-strain hardening coefficient (PSH) (i.e., J′b/Jtip), the more saturated the crack distribution. The higher initial fracture strength indicates that the matrix has higher fracture toughness. Therefore, for embodiment 2 with Na2CO3substitution of 0.75Na2O %, the reduced initial fracture strength makes it show a more saturated fracture distribution than embodiment 1. However, although the initial crack strength of UHP-EGC (embodiment 3) continues to decrease with the further increase of Na2CO3substitution, the excessive Na2CO3substitution will reduce the bridging effect between the fiber and the matrix, thus reducing the crack control capability of UHP-EGC (manifested as less crack number and larger crack width). For the Modulus Series, the increase of initial crack strength significantly reduces the saturated cracking behavior of UHP-EGC, and the number of cracks is significantly reduced. The initial crack strength of the comparative embodiment 1 and comparative embodiment 2 is reduced by 1.3 MPa and 1.0 MPa respectively compared with that of the embodiment 1, the addition order of nano calcium carbonate effects the density of the matrix, thereby reducing the initial crack performance.

It can be seen from the part b inFIG.8that the tensile strength of UHP-EGC exceeds 8 MPa, and the use of Na2CO3has a positive effect on the tensile strength. The tensile strength of embodiments 2 and 3 is more than 10 MPa, which is 27.2% and 22.2% higher than that of embodiment 1, respectively. The tensile strength of the comparative embodiment 1 and comparative embodiment 2 is reduced by 2.0 MPa and 1.1 MPa, respectively compared with that of embodiment 1, the addition order of nano calcium carbonate effected the fiber bonding performance, resulting in a decrease in the fiber bridging capability in the limit state, thereby reducing the tensile strength.

It can be seen from the part c inFIG.8that the substitution amount of Na2CO3is 0.75Na2O %, the crack control capability of UHP-EGC is improved, but the overall deformation capability is limited, and the ultimate tensile strain of embodiment 2 is only 6.13%. Although increasing the modulus of the activator reduces the crack control capability, the embodiment 4 shows the highest deformation capability, and the ultimate tensile strain reaches 8.58%, which is 31.6% higher than the embodiment 1. The ultimate tensile strain of comparative embodiment 1 and comparative embodiment 2 is reduced to 4.8% and 5.9% respectively compared with that of embodiment 1, and the addition order of nano calcium carbonate has a significant effect on the tensile deformation capability.

It can be seen from the part d inFIG.8that in Na2CO3Series, the ultimate tensile strain of embodiment 2 is close to that of embodiment 1, and its strain energy is only 416.8 kJ m−3, which is only 6.2% higher than that of embodiment 1. However, when the substitution amount of Na2CO3is 1.5Na2O %, the strain energy of embodiment 3 is significantly increased to 518.5 kJ m−3, which is 32.2% higher than that of embodiment 1. In addition, it can be seen from the Modulus Series that increasing the modulus of the activator significantly improves the energy dissipation capacity of UHP-EGC. Embodiment 4 and embodiment 5 increase the strain energy due to the increase of deformation capacity. The strain energy of embodiment 5 reaches 564.1 kJ m−3, which is 43.8% higher than that of embodiment 1. The addition of Na2CO3reduces the initial crack strength but is beneficial to the tensile strength, while increasing the modulus of the activator increases the initial crack strength but reduces the crack control ability.

Proper adjustment of these parameters can optimize the cracking behavior and tensile properties of UHP-EGC. The strain energy of comparative embodiment 1 and comparative embodiment 2 is reduced by 18% and 13% respectively compared with that of embodiment 1, the initial crack strength, tensile strength, and tensile deformation capability are significantly reduced by changing the addition order of nano calcium carbonate, so the strain energy (i.e., the envelope area of the tensile curve) is relatively reduced.

4. Carbon emission

The use of Na2CO3greatly reduces the amount of Na2SiO3solution and NaOH, which is of great significance for reducing the carbon footprint of geopolymer concrete materials. In order to quantify the influence of the change of activator on the environmental performance of UHP-EGC, the environmental performance of UHP-EGC is comprehensively discussed by considering the tensile properties and carbon emissions. Table 3 shows the carbon emission factor of UHP-EGC and the total carbon emission per unit volume of concrete. It should be noted that the carbon emission factor of raw materials only considers the carbon emissions generated in the production process. Therefore, the carbon emission factor of the Na2SiO3solution is set to 1.222 kg CO2-e/kg.

TABLE 3EmissionMix IDcoefficientEmbodimentEmbodimentEmbodimentEmbodimentEmbodimentMaterials(kg CO2-e/kg12345S105 slag0.01915.5815.5815.5815.5815.58Class F fly ash0.0092.2372.2372.2372.2372.237Silica fume000000NaOH1.91583.9675.2766.3269.8355.61Na2SiO31.222433.3388.1342.5479.2524.8Na2CO30.111/1.6573.325//Quartz sand0.014.0664.0664.0664.0664.066Ultra-high238.8038.8038.8038.8038.80molecularweightpolyethylenefiberCO2-e/578.0525.7472.9609.7641.1(kg CO2-e/m3)

FIG.9shows the carbon emissions of each raw material per cubic meter of UHP-EGC obtained from embodiments 1-5.FIG.9indicates that the carbon emissions of the activator account for the first place in the carbon emissions of UHP-EGC raw materials, about more than 87%. In embodiment 1, Na2SiO3accounted for 75.0% of the total carbon emissions, while the carbon emissions of NaOH—Na2SiO3activator accounted for 89.5%. The CO2-e of embodiment 1 reached 578.0 kg CO2-e/m3, and the carbon emission of UHP-EGC is significantly reduced by replacing some activators with Na2CO3, and the carbon emission of embodiment 3 is 18.2% lower than that of embodiment 1. On the other hand, increasing the modulus of the activator means that the amount of Na2SiO3needs to be increased, which leads to an increase in carbon emissions. When the modulus of the activator is increased to 1.65, the CO2-e of embodiment 4 reaches 641.1 kg CO2-e/m3, an increase of 10.9%. The carbon emissions of comparative embodiment 1 and comparative embodiment 2 are the same as those of embodiment 1, and the addition order of nano calcium carbonate has no effect on carbon emissions.

5. Nano calcium carbonate is used to fill the pores, too early or too late to join will lead to a decrease in mechanical properties. Compared with embodiment 1, the compressive strength of the comparative embodiment 1 and comparative embodiment 2 decreased by 5-10 MPa, the crack width increased by 7%-12%, the initial crack strength decreased by 1-1.3 MPa, the tensile strength decreased by about 1.1-2.0 MPa, the tensile strain decreased to 4.8% and 5.9%, and the strain energy decreased by 13%-18%, but the setting time and carbon emission are not effected.

The above is only the preferred embodiments of this application, rather than limiting the same, any modified or equivalently replaced that can be easily appreciated by technical personnel familiar with this technical field within the technical scope disclosed in this application should be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claim.