Waterwork concrete using waste oyster shell powder and preparation method thereof

Abstract

This invention provides a hydraulic concrete utilizing waste oyster shell powder and its preparation method, belonging to the field of concrete and resource recycling technology. The hydraulic concrete utilizing waste oyster shell powder provided by this invention is prepared from the following raw materials in parts by weight: 100 parts cement, 5-15 parts oyster shell powder, 10-30 parts silica fume, 200-300 parts fine aggregate, 800-1000 parts coarse aggregate, 40-50 parts water, and 0.5-1.5 parts water-reducing agent. The oyster shell powder is ground to a particle size ≤90μm and then calcined at 800-950°C for 1.5 hours. This concrete not only increases the 28-day compressive strength by 12.8% compared to ordinary concrete, but also possesses good resistance to sulfate attack and high impermeability, while efficiently utilizing waste oyster shell powder.

Description

Technical Field

[0001] This invention relates to the field of concrete and resource recycling technology, and in particular to a hydraulic concrete using waste oyster shell powder and its preparation method. Background Technology

[0002] Cement, as the core binder of concrete, has significant energy consumption and carbon emissions during its production process, making it one of the major sources of greenhouse gas emissions in the construction industry. Meanwhile, discarded oyster shells not only occupy land resources, but also breed bacteria and release harmful gases such as hydrogen sulfide (H2S) and ammonia (NH3) during their natural decomposition, posing a significant threat to the surrounding environment and human health.

[0003] To address the aforementioned issues, existing research proposes using oyster shells, after pretreatment including washing, calcination, and fine grinding, as an auxiliary cementitious material to partially replace cement. Calcination effectively enhances the pozzolanic activity of oyster shell powder, enabling it to react with cement hydration products in an alkaline environment. Experiments show that when the amount of oyster shell powder replacing cement is between 5% and 15%, the resulting concrete not only exhibits enhanced mechanical properties but also improved resistance to sulfate attack. However, this technological approach currently faces limitations such as a narrow dosage range and an unclear activation mechanism, hindering the large-scale utilization of oyster shells.

[0004] Therefore, developing an efficient utilization method that can effectively increase the content of oyster shell powder, clarify its hydration and strengthening mechanism, and is applicable to the preparation of green concrete has become the key to promoting the development of resource utilization and application technology of this waste. Summary of the Invention

[0005] The purpose of this invention is to provide a hydraulic concrete utilizing waste oyster shell powder and its preparation method. The hydraulic concrete utilizing waste oyster shell powder provided by this invention not only increases the 28-day compressive strength by 12.8% compared to ordinary concrete, but also possesses excellent resistance to sulfate attack and high impermeability, while simultaneously achieving efficient utilization of waste oyster shell powder.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a hydraulic concrete using waste oyster shell powder, characterized in that it is prepared from the following raw materials in parts by weight: 115-145 parts of cementitious material, 1000-1300 parts of aggregate, 0.5-1.5 parts of water-reducing agent, and 40-50 parts of water.

[0008] The cementitious material comprises 100 parts cement, 5-15 parts oyster shell powder, and 10-30 parts silica fume; the oyster shell powder accounts for 3.7-12% of the total mass of the cementitious material.

[0009] The water-cement ratio of the hydraulic concrete utilizing waste oyster shell powder is 0.27~0.43.

[0010] Preferably, the oyster shell powder comprises the following components by mass percentage: 95-97% CaCO3, less than 1% Al2O3, less than 1% MgO, less than 1% SO2, less than 1% Na2O, less than 0.5% SrO, less than 0.05% P2O5, and less than 1% SO3;

[0011] Preferably, the cement accounts for 69-87% of the total mass of the cementitious materials.

[0012] Preferably, the oyster shell powder has a particle size of less than 90 μm.

[0013] Preferably, the oyster shell powder is obtained by crushing and grinding waste oyster shells: the waste oyster shells are washed in running water for 1 hour and then dried in a 100-degree oven for 3 hours; the dried waste oyster shells are crushed into fragments smaller than 10mm and then ground with a ball mill to obtain oyster shell powder with a particle size of less than 90μm.

[0014] Preferably, the oyster shell powder with a particle size of less than 90 μm after grinding should be calcined at 950°C for 1.5 hours before preparing hydraulic concrete to obtain activated oyster shell powder.

[0015] The present invention also provides a method for preparing hydraulic concrete using waste oyster shell powder as described in the above technical solution, comprising: mixing cementitious materials, aggregates, water-reducing agents and water to obtain hydraulic concrete using waste oyster shell powder.

[0016] This invention provides a hydraulic concrete utilizing waste oyster shell powder, prepared from the following raw materials in parts by weight: 115-145 parts of cementitious material, 1000-1300 parts of aggregate, 0.5-1.5 parts of water-reducing agent, and 40-50 parts of water; the cementitious material includes 100 parts of cement, 5-15 parts of oyster shell powder, and 10-30 parts of silica fume; the oyster shell powder accounts for 3.7-12% of the total mass of the cementitious material; the water-cement ratio of the hydraulic concrete utilizing waste oyster shell powder is 0.27-0.43. This invention, by adding calcined and activated waste oyster shell powder, together with silica fume as auxiliary cementitious materials, exerts a micro-aggregate filling effect and a pozzolanic effect during cement hydration. The active CaO component in the oyster shell powder can react with the active... and cement hydration products A secondary hydration reaction occurs, accelerating the generation of more low-calcium-silica CSH gel, effectively optimizing the paste-aggregate interface structure. This significantly improves the later-stage compressive strength and density of concrete while replacing a portion of the cement. Simultaneously, by precisely controlling the water-cement ratio within the range of 0.27~0.43 and matching an appropriate amount of water-reducing agent, this invention ensures the full hydration of the cementitious materials, resulting in excellent workability of the fresh concrete and promoting the refinement and uniform distribution of the internal pore structure. After hardening, internal defects in the concrete are reduced, and the microstructure is more compact. This not only directly contributes to the improvement of the concrete's compressive strength but also significantly enhances its resistance to sulfate attack and impermeability, thus ensuring that the overall durability of the concrete meets the long-term service requirements of hydraulic structures.

[0017] The results of the embodiments show that the hydraulic concrete utilizing waste oyster shell powder provided by the present invention has a 28-day compressive strength between 35.1 and 39.6 MPa and a flexural strength between 4.5 and 5.3 MPa. When the oyster shell powder content is 6%, the 28-day compressive strength of the concrete reaches the highest of 39.6 MPa, which is 12.8% higher than the baseline group. Simultaneously, its resistance to sulfate attack significantly improves with increasing oyster shell powder content, and the mass loss rate decreases from 4.8% in the baseline group to 3.2% at a content of 10%. All embodiments meet the requirement of impermeability grade P8 or higher. Furthermore, the calcined oyster shell powder in the present invention accounts for 3.7% to 12% of the cementitious material, achieving efficient resource utilization of waste oyster shells. Therefore, this hydraulic concrete achieves excellent mechanical properties while also possessing improved resistance to sulfate attack and high impermeability, providing an effective way for the large-scale, high-value application of waste oyster shells. Detailed Implementation

[0018] This invention provides a hydraulic concrete utilizing waste oyster shell powder, prepared from the following raw materials in parts by weight: 115-145 parts of cementitious material, 1000-1300 parts of aggregate, 0.5-1.5 parts of water-reducing agent, and 40-50 parts of water; the cementitious material includes cement, oyster shell powder, and silica fume; the oyster shell powder accounts for 3.7-12% of the total mass of the cementitious material; the water-cement ratio of the hydraulic concrete utilizing waste oyster shell powder is 0.27-0.43.

[0019] The raw materials for preparing the hydraulic concrete using waste oyster shell powder according to the present invention include 115-145 parts of cementitious material by weight. The above formula is preferably 117-126 parts of cementitious material, and more preferably 120-125 parts of cementitious material.

[0020] By controlling the content of cementitious materials within the above-mentioned range, this invention can generate an appropriate amount of CSH gel to fill the gaps in concrete materials, thereby improving the strength and impermeability of concrete materials. It ensures that a sufficient amount of CSH gel is generated to fully fill the gaps in concrete materials, thus avoiding insufficient improvement in material strength; it also avoids the excessive filling of gaps by secondary reaction products, which would lead to material expansion and cracking.

[0021] In this invention, the cementing materials include cement, oyster shell powder, and silica fume. This invention utilizes oyster shell powder and silica fume as auxiliary cementing materials for cement, saving on cementing material costs while also enabling solid waste utilization, energy conservation, and emission reduction, thus improving resource utilization. Furthermore, this invention utilizes the synergistic effect of silica fume and oyster shell powder to improve the component ratio of concrete and enhance its impermeability.

[0022] In this invention, the cement preferably accounts for 75-85% of the total mass of the cementitious materials. By using cement as the main cementitious material and controlling its dosage within the above range, this invention can ensure that the concrete has high compressive strength and durability.

[0023] In this invention, the cement preferably includes the most common PO42.5 cement, or other commonly used cements that do not disrupt its specific hydration reaction process. The PO42.5 cement and other cements meeting the requirements of this patent independently preferably include cement clinker with a mass percentage >85%; the cement clinker preferably includes tricalcium silicate with a mass percentage of 45-60%, more preferably 50-55%; the activity index of the tricalcium silicate is preferably: when the silicate cement clinker contains 55±5% by mass of tricalcium silicate, the 3-day compressive strength of the silicate cement clinker is >20 MPa, and the 28-day compressive strength is >50 MPa. In this invention, the 3-day compressive strength of the cement is preferably >22 MPa, and the 28-day compressive strength of the cement is preferably >55 MPa. The present invention selects the above-mentioned type of cement, which can utilize the high content of tricalcium silicate in the cement clinker to enable the cement to have high early hydration activity and strength development rate, thereby forming a good synergistic effect with auxiliary cementitious materials such as oyster shell powder and silica fume, and further optimizing the mechanical properties and durability of hydraulic concrete.

[0024] In this invention, the mass fraction of the oyster shell powder is 5-15 parts, preferably 5-10 parts, and most preferably 5-7 parts. By using oyster shell powder as a cementing material and controlling its dosage within the above range, this invention allows it to work together with silica fume as an auxiliary cementing material. When the dosage of oyster shell powder is within this optimal range, its micro-aggregate filling effect, pozzolanic activity effect, and crystal nucleation effect can achieve ideal synergy, thereby significantly improving concrete performance while achieving optimal utilization of waste resources.

[0025] In this invention, the particle size of the oyster shell powder is preferably less than 45 μm. By controlling the particle size of the oyster shell powder within this range, the present invention enables it to have a high specific surface area, allowing for sufficient contact with the mineral powder and cement to undergo a hydration reaction, thereby effectively improving the strength and durability of concrete. Furthermore, during the calcination stage, the uniformity of calcination can be ensured, preventing excessive surface burning and uneven internal heating of the oyster shell powder.

[0026] In this invention, the oyster shell powder comprises the following components by mass percentage: 95-97% CaCO3, less than 1% Al2O3, less than 1% MgO, less than 1% SO2, less than 1% Na2O, less than 0.5% SrO, less than 0.05% P2O5, and less than 1% SO3. By using oyster shell powder with the above-mentioned components and contents within the aforementioned range, this invention enables it to possess higher hydration activity, higher utilization rate, and is more conducive to improving the strength and durability of concrete.

[0027] In this invention, preferably, the amount of silica fume can be 1.5 to 1.8 times that of oyster shell powder. By controlling the amount of silica fume within the above range, this invention enables it to better cooperate with oyster shell powder to activate its hydration reaction, thereby improving the strength and durability of concrete.

[0028] The raw materials for preparing the hydraulic concrete using waste oyster shell powder according to the present invention include 1,000 to 1,300 parts of aggregate, preferably 1,000 to 1,200 parts, and more preferably 1,000 to 1,100 parts, by weight.

[0029] In this invention, the aggregate preferably includes river sand and gravel; the river sand preferably accounts for 25% of the total mass of the aggregate. By controlling the amount of river sand and gravel in the aggregate within the above-mentioned range, this invention enables them to better exert their synergistic effect, improve the density of concrete, and thus give the concrete higher strength and durability.

[0030] In this invention, the river sand is preferably zone II medium sand; the fineness modulus of the river sand is preferably 2.72 (medium sand). This invention does not have special requirements regarding the source of the river sand; commercially available materials well-known in the art can be used. By selecting the above-mentioned type of river sand, this invention enables it to fully contact the aggregate, improving the density of the concrete and thus giving the concrete higher strength and durability.

[0031] In this invention, the preferred particle size of the aggregate is 5-25 mm; the preferred gradation of the aggregate is continuous gradation. This invention does not have special requirements regarding the source of the aggregate; commercially available materials well-known in the art can be used. By controlling the aggregate particle size within the above range, this invention enables it to fully contact river sand, improving the density of the concrete and thus giving the concrete higher strength and durability.

[0032] The raw materials for preparing the hydraulic concrete using waste oyster shell powder according to the present invention, by weight percentage, include 1% water-reducing agent, preferably 0.08-0.09%. By adding water-reducing agent and controlling its dosage within the above range, the present invention can ensure that the concrete has high fluidity while reducing water consumption, which is more conducive to the solidification and molding of the concrete and reduces cracks formed by water evaporation, thereby enabling the concrete to obtain higher early strength and ensure that the concrete has high durability.

[0033] In this invention, the water-reducing agent preferably comprises a polyester-based polycarboxylate water-reducing agent. This invention does not have special requirements regarding the source of the water-reducing agent; commercially available materials well-known in the art can be used.

[0034] The raw materials for preparing the hydraulic concrete using waste oyster shell powder according to the present invention include a surplus of water, by weight parts.

[0035] The present invention does not have any special requirements for the source of the water; concrete mixing water, which is well known in the art, can be used.

[0036] In this invention, the water-cement ratio of the hydraulic concrete utilizing waste oyster shell powder is 0.27~0.43, preferably 0.31~0.41, and more preferably 0.35~0.39. By controlling the water-cement ratio within the above range, this invention ensures that the cementitious materials and water undergo sufficient hydration reaction while maintaining the workability of the concrete, and prevents cracking due to water evaporation during early hardening, thereby giving the concrete high strength and durability.

[0037] The hydraulic concrete using waste oyster shell powder provided by this invention has a high proportion of oyster shell powder in the cementitious material, which not only enables efficient resource reuse of oyster shell powder, but also has high strength, ultra-high durability and stability.

[0038] The present invention also provides a method for preparing hydraulic concrete using waste oyster shell powder as described in the above technical solution, comprising: mixing cementitious materials, aggregates, water-reducing agents and water to obtain hydraulic concrete using waste oyster shell powder.

[0039] This invention does not have special requirements for the mixing operation; any concrete mixing method known in the art can be used to ensure that the concrete is mixed evenly.

[0040] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] Example 1

[0042] A type of hydraulic concrete utilizing waste oyster shell powder is prepared from the following raw materials in parts by weight: 115-145 parts of cementitious material, 1000-1300 parts of aggregate, 0.5-1.5 parts of water-reducing agent, and 40-50 parts of water.

[0043] The cementitious material includes cement, oyster shell powder, and silica fume; wherein, the cement is selected as PO42.5 cement (including cement clinker with a mass percentage >85%; the cement clinker preferably includes 45-60% tricalcium silicate by mass, more preferably 50-55% tricalcium silicate by mass; the activity index of the tricalcium silicate is preferably: when the silicate cement clinker contains 55±5% tricalcium silicate by mass, the 3-day compressive strength of the silicate cement clinker is >20MPa, and the 28-day compressive strength is >50MPa); the 3-day compressive strength of the cement is 10MPa, and the 28-day compressive strength is 42.5MPa, and the mass percentage of cement is preferably 75-85% of the total mass of the cementitious material. The mass percentage of the oyster shell powder is 3.7-12% of the total mass of the cementitious material; the particle size of the oyster shell powder is preferably less than 45μm. The chemical composition and content of the oyster shell powder are shown in Table 1.

[0044] The water-cement ratio of the hydraulic concrete utilizing waste oyster shell powder is 0.27~0.43.

[0045] The aggregate consists of river sand and gravel; the river sand accounts for 25% of the total aggregate mass, and is preferably medium sand from Zone II with a fineness modulus of 2.72; the gravel accounts for 75% of the total aggregate mass, and the gravel has a particle size of 5-25 mm and is continuously graded.

[0046] The water-reducing agent is selected from polyester polycarboxylate water-reducing agents.

[0047] The method for preparing hydraulic concrete using waste oyster shell powder is as follows: Cementitious materials, aggregates, water-reducing agents, and water are mixed and stirred in a mixer for 3 minutes to obtain hydraulic concrete using waste oyster shell powder. The concrete is then poured into a 150×150×150mm mold and cured at room temperature (20±0.5℃) for 24 hours before demolding. Performance tests are then conducted under standard conditions (temperature 20±0.5℃, relative humidity above 95%) for 3 days, 7 days, and 28 days respectively.

[0048] Table 1. Chemical composition and content (mass percentage / %) of oyster shell powder in Example 1

[0049] Concrete performance testing:

[0050] The test used the following mixing ratio:

[0051] The mixtures obtained from the above mix proportions were stirred evenly, poured, vibrated, demolded, and cured to prepare hydraulic concrete with performance requirements. For each mix proportion, three specimens were tested as a group according to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2002) and the long-term immersion method (Chinese Standard GB / T 50082-2009). The average value of the test results for each group is as follows:

[0052] The above experimental examples show that, under this mix proportion, as the amount of oyster shell powder added increases, the compressive strength and flexural strength of the concrete exhibit a trend of first increasing and then decreasing, while the mass loss due to sulfate attack decreases with the addition of oyster shell powder. At an addition of 6%, the overall performance of the concrete is optimal, improving both its mechanical properties and its impermeability. During the grinding and calcination of oyster shell powder, the main component transforms from CaCO3 to calcium oxide and participates in the subsequent hydration reaction. This hydration reaction makes the concrete more compact, thus improving both mechanical properties and impermeability. However, because this hydration reaction is relatively slow, adding a large amount of calcined oyster shell powder can lead to incomplete early reactions. Even after the concrete has set, the hydration reaction continues, excessively filling gaps and causing the expansion of microcracks. This is also the main reason for the reduced strength. Therefore, the mechanical performance of this concrete varies under different mix proportions.

Claims

1. A type of hydraulic concrete utilizing waste oyster shell powder, characterized in that, It is prepared from the following raw materials in parts by weight: 115-145 parts cementitious material, 1000-1300 parts aggregate, 0.5-1.5 parts water-reducing agent and 40-50 parts water; The cementitious material comprises 100 parts cement, 5-15 parts oyster shell powder, and 10-30 parts silica fume; the oyster shell powder accounts for 3.7-12% of the total mass of the cementitious material. The water-cement ratio of the hydraulic concrete utilizing waste oyster shell powder is 0.27~0.43; The oyster shell powder comprises the following components by mass percentage: 95-97% CaCO3, less than 1% Al2O3, less than 1% MgO, less than 1% SO2, less than 1% Na2O, less than 0.1% SrO, less than 0.05% P2O5, and less than 1% SO3; The cement accounts for 69-87% of the total mass of the cementitious materials.

2. The hydraulic concrete as described in claim 1, characterized in that, The oyster shell powder has a particle size of less than 90 μm.

3. The hydraulic concrete as described in claim 1, characterized in that, The oyster shell powder is obtained by crushing and grinding waste oyster shells. The discarded oyster shells were washed in running water for 1 hour and then dried in a 100-degree oven for 3 hours. The dried waste oyster shells are crushed into fragments smaller than 10 mm and then ground using a ball mill to obtain oyster shell powder with a particle size of less than 90 μm.

4. The hydraulic concrete as described in claim 1, characterized in that, The oyster shell powder with a particle size of less than 90 μm after grinding should be calcined at 950°C for 1.5 hours before preparing hydraulic concrete to obtain activated oyster shell powder.

5. The method for preparing hydraulic concrete according to any one of claims 1 to 4, characterized in that, include: By mixing cementitious materials, aggregates, water-reducing agents, and water, hydraulic concrete utilizing waste oyster shell powder is obtained.

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