A dry hard concrete curb and a method for manufacturing the same

Abstract

The application discloses a dry hard concrete curb and a preparation method thereof. Components of the dry hard concrete curb include cement, fly ash, iron tailing sand, 3-5mm iron tailing stone, 5-8mm gravel, water, polycarboxylic acid water reducing agent and modified PVC heat shrinkage film powder. The modified PVC heat shrinkage film powder is cut into pieces in liquid nitrogen, mixed with the iron tailing sand, and then ball milled in a dry environment. The shrinkage force generated by the shrinkage performance of the PVC heat shrinkage film itself under the high temperature condition of steam curing resists the thermal expansion effect in the steam curing process. Through optimization and adjustment of the PVC particle size, the mixing amount and the steam curing temperature, the static curing process is omitted, the heating rate does not need to be controlled, the temperature control requirement in the steam curing process is greatly optimized, and the performance of the curb is ensured.

Description

Technical Field

[0001] This invention relates to the field of building material product preparation and production, specifically to a dry-hardened concrete curbstone and its preparation method. Background Technology

[0002] Dry-hard concrete curbstone is a type of concrete curbstone prepared under conditions of low water-cement ratio and high molding pressure. It has high density, high strength of the green body after molding, and can be demolded immediately in a wet state, which can greatly improve the turnover speed of molds and increase production efficiency.

[0003] After dry-hard concrete curb stones are pressed into shape, steam curing is typically used to improve their early strength, product quality, and delivery efficiency. The static curing time during steam curing significantly impacts the mechanical properties and durability of the concrete. Static curing primarily aims to enhance the initial structural strength of the concrete block, enabling it to better withstand the thermal expansion during steam curing and avoid adverse effects on the concrete structure. Insufficient static curing time will have a significant negative impact on concrete strength development. However, extending the static curing time greatly increases the steam curing duration and cost, which is detrimental to production efficiency. Therefore, minimizing the static curing time and accelerating the heating rate are the main methods to shorten the steam curing time and improve efficiency. However, reducing the static curing time and accelerating the heating rate requires addressing the adverse effects of increased temperature on the concrete structure during steam curing. Currently used techniques include reducing the water-cement ratio, increasing concrete density, and using aggregates with lower expansion rates. However, these methods not only limit the types of raw materials available for dry-hard concrete curb stones but also have limited effectiveness in improving their properties. Summary of the Invention

[0004] In view of the problems existing in the background technology, the present invention provides a dry-hardened concrete curbstone and its preparation method, which can eliminate the static curing time and eliminate the need to control the heating process, thereby greatly improving the steam curing efficiency and curbstone production efficiency.

[0005] This invention provides a dry-hardened concrete curbstone, wherein the amounts of each component in each cubic meter of dry-hardened concrete curbstone are as follows:

[0006]

[0007] The modified PVC heat shrink film powder is prepared as follows: PVC heat shrink film tailings are cut into strips with a width not exceeding 2 mm and a length not exceeding 4 mm. These strips are then immersed in liquid nitrogen and fully soaked. After being removed, they are mixed with iron tailings sand and rapidly ball-milled for 3-5 minutes under dry conditions to break them into powder with a particle size not exceeding 50 μm, thus forming modified PVC heat shrink film powder. After being soaked in liquid nitrogen, the PVC heat shrink film quickly hardens and becomes brittle. Further mixing it with iron tailings sand and grinding it under dry conditions will immediately turn it into powder. If it is not soaked in liquid nitrogen, the heat shrink film has a large shrinkage and cannot be ground into powder.

[0008] The mass fractions of PVC heat shrink film tailings and iron tailings are:

[0009] One portion of PVC heat shrink film waste.

[0010] 50-200 parts of iron tailings sand;

[0011] The thickness of the PVC heat shrink film tailings is 0.02 to 0.05 mm.

[0012] The cement is P.O42.5 ordinary Portland cement that conforms to the current national standard GB 175 "General Portland Cement";

[0013] The fly ash is Grade II or Grade I fly ash as specified in the current national standard GB / T 1596 "Fly Ash for Cement and Concrete".

[0014] The crushed stone conforms to the relevant provisions of the current industry standard "Standard for Quality and Testing Methods of Sand and Stone for Ordinary Concrete" JGJ 52.

[0015] The iron tailings sand is fine sand with a fineness modulus of 2.0 to 2.2 as specified in the current national standard "Iron Tailings Sand" GB / T 31288. If the particle size is too fine, it will affect the aggregate gradation and the performance of concrete.

[0016] The polycarboxylate superplasticizer is a superplasticizer that complies with the relevant provisions of the current industry standard "Carboxylic Acid-Based High-Performance Superplasticizers" JG / T 223.

[0017] The present invention also provides a method for preparing the dry-hardened concrete curbstone, comprising:

[0018] (1) Mix the modified PVC heat shrink film powder, cement, fly ash, iron tailings sand, iron tailings ore, and crushed stone evenly according to the above proportions to form solid material A;

[0019] (2) Add the polycarboxylate superplasticizer and water to the above solid material A at the same time, stir evenly to form a mixed wet material B;

[0020] (3) Pour the wet mixture B from step (2) into the mold, control the load to 10-12MPa, and press it into a curbstone blank;

[0021] (4) Place the curbstone blank in a steam curing chamber for curing. There is no need for static curing or temperature setting. Simply place the blank in a curing chamber with the temperature controlled at 70-75℃. After steam curing for 6-12 hours, take it out and cure it for 28 days to prepare dry hard concrete curbstone.

[0022] Beneficial effects:

[0023] In the steam curing process of concrete, raw materials with low expansion are generally used. Iron tailings have a higher linear thermal expansion than limestone aggregates, which is detrimental to the structural stability of concrete during steam curing and is generally not used. This invention aims to reduce the thermal expansion during the steam curing process, enabling the utilization of iron tailings in dry-hard concrete curb stones, eliminating the need for static curing time and temperature control, and optimizing the process by using modified PVC heat-shrinkable film powder as an anti-thermal expansion material. The shrinkage force generated by the shrinkage properties of the PVC heat-shrinkable film itself under the high-temperature conditions of steam curing resists the thermal expansion during steam curing. Furthermore, through optimization of PVC particle size and dosage, as well as optimized adjustment of the steam curing temperature, the static curing process is eliminated, and the temperature rise rate does not need to be controlled, greatly optimizing the temperature control requirements during steam curing while ensuring the performance of the curb stones. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments.

[0025] Example 1:

[0026] A dry-hardened concrete curbstone, the proportions of each component in each cubic meter of dry-hardened concrete curbstone are as follows:

[0027]

[0028]

[0029] The modified PVC heat shrink film powder is prepared by cutting 1 part of PVC heat shrink film tailings into strip-shaped fragments with a width of 2 mm and a length of 4 mm, immersing them in liquid nitrogen, taking them out after full wetting, mixing them with 50 parts of iron tailings sand, and then rapidly ball milling them for 3 minutes under dry conditions to break them into powder with a particle size of 45 μm, thus forming modified PVC heat shrink film powder.

[0030] The aforementioned steam curing process for dry-hard concrete curb stones involves steam curing at 73℃ for 9 hours with a curing humidity of 95%. Curb stones are obtained under these conditions.

[0031] Example 2:

[0032] A dry-hardened concrete curbstone, wherein the proportions of each component per cubic meter of the dry-hardened concrete curbstone are as follows:

[0033]

[0034] The modified PVC heat shrink film powder is prepared by cutting 1 part of PVC heat shrink film tailings into strips with a width of 2mm and a length of 2mm, immersing them in liquid nitrogen, taking them out after they are fully wetted, mixing them with 200 parts of iron tailings sand, and then rapidly ball milling them for 5 minutes under dry conditions to break them into powder with an average particle size of 20μm, thus forming modified PVC heat shrink film powder.

[0035] The aforementioned steam curing process for dry-hard concrete curb stones involves steam curing at 70℃ for 9 hours with a curing humidity of 95%. Curing under these conditions yields the curb stones.

[0036] Example 3:

[0037] A dry-hardened concrete curbstone, wherein the proportions of each component per cubic meter of the dry-hardened concrete curbstone are as follows:

[0038]

[0039] The modified PVC heat shrink film powder is prepared by cutting 1 part of PVC heat shrink film tailings into strips with a width of 1 mm and a length of 3 mm, immersing them in liquid nitrogen, taking them out after they are fully wetted, mixing them with 100 parts of iron tailings sand, and then rapidly ball milling them for 4 minutes under dry conditions to break them into powder with an average particle size of 35 μm, thus forming modified PVC heat shrink film powder.

[0040] The aforementioned steam curing process for dry-hard concrete curb stones involves steam curing at 75℃ for 9 hours with a curing humidity of 95%. Curing under these conditions yields the curb stones.

[0041] Comparative Example 1

[0042] Same as Example 3, except that modified PVC heat shrink film powder is not added.

[0043] Comparative Example 2

[0044] Same as Example 3, except that 1.5 kg / m³ is added. 3 Modified PVC heat shrink film powder.

[0045] Comparative Example 3

[0046] Similar to Example 3, the difference is that the PVC powder added is not subjected to liquid nitrogen and grinding treatment, but is only cut and added to dry hard concrete.

[0047] Comparative Example 4

[0048] Same as Example 3, except that the steam curing temperature is 60°C.

[0049] Comparative Example 5

[0050] Same as Example 3, except that the steam curing temperature is 80°C.

[0051] Comparative Example 6

[0052] Similar to Example 3, except that a static curing time of 4 hours is performed before constant temperature curing.

[0053] Comparative Example 7

[0054] Same as Example 3, except that the heating rate is controlled at 5°C / h.

[0055] Comparative Example 8

[0056] Same as Example 3, except that the heating rate is controlled at 20℃ / h.

[0057] Comparative Example 9

[0058] Similar to Example 3, except that no modified PVC heat shrink film powder is added, and the heating rate is controlled at 5℃ / h.

[0059] Comparative Example 10

[0060] Similar to Example 3, except that no modified PVC heat shrink film powder is added, and the heating rate is controlled at 20℃ / h.

[0061] Comparative Example 11

[0062] Similar to Example 3, the difference is that the PVC powder added is directly ground during liquid nitrogen and grinding treatment, without being mixed with iron tailings sand.

[0063] Comparative Example 12

[0064] Similar to Example 3, except that the PVC is cut into pieces with a length of 2cm and a width of 1cm, then cooled and ground with liquid nitrogen, and is not mixed with iron tailings sand.

[0065] The compressive strength (compressive strength at the time of removal from the curing kiln after steam curing) and 28-day compressive strength (compressive strength after 28 days of continued curing) of the above embodiments and comparative examples were tested. Before testing the compressive strength, the test blocks were removed from the curing room when they reached the required curing age, placed at room temperature for 1 hour, and then cut into 100*100*100mm blocks from the middle. The tests were then conducted according to the requirements of GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The indicators are shown in Table 1.

[0066] Table 1 Curbstone Indicators for Each Embodiment and Comparative Example

[0067]

[0068]

[0069] As shown in Table 1, Comparative Example 1 shows that without the addition of modified PVC heat shrink film powder, and without static curing, the internal structure of the concrete is defective due to the thermal expansion during steam curing, resulting in microcracks. This leads to a significant decrease in both the concrete's compressive strength at the kiln and its 28-day compressive strength.

[0070] As can be seen from Comparative Example 2, the addition of excessive PVC heat-shrinkable film powder increases the porosity of the concrete and reduces its strength. Furthermore, the excessive shrinkage of the heat-shrinkable film causes excessive shrinkage in the structure, which also affects the stability of the concrete structure.

[0071] As can be seen from Comparative Example 3, simply cutting the PVC heat-shrinkable film tailings without crushing and grinding them is insufficient to effectively resist the thermal expansion of the concrete structure. This is mainly because, after cutting, the PVC is relatively large and unevenly distributed in the concrete, failing to adequately resist the adverse effects of thermal expansion. However, when the heat-shrinkable film is powdered, it is evenly distributed in the aggregate, thus uniformly resisting the adverse effects of thermal expansion from iron tailings sand and iron tailings ore.

[0072] As can be seen from Comparative Example 4, the steam curing temperature is too low, which prevents the PVC heat shrink film powder from achieving proper heat shrinkage and is insufficient to resist the adverse effects of thermal expansion. As can also be seen from Comparative Example 5, the steam curing temperature is too high, which causes the shrinkage to be too fast and also has an adverse effect on the structure, although the effect is slightly smaller.

[0073] As can be seen from Comparative Example 6, under the condition of a fixed steam curing time, the longer the static curing time, the shorter the constant temperature process time. Under this condition, the early hydration reaction is slower, resulting in a lower compressive strength after kiln firing. However, the 28-day strength is relatively high, but still lower than that of curbstone optimized with modified PVC powder. Moreover, the low early strength is not conducive to improving production efficiency.

[0074] Comparative Examples 7, 8, 9, and 10 show that different heating rates do not affect concrete performance when temperature control is implemented. However, without PVC, the higher the heating rate, the lower the kiln-exit compressive strength and 28-day compressive strength. This indicates that incorporating modified PVC can effectively resist the adverse effects on the structure caused by excessively rapid heating rates, large internal and external temperature differences, and inconsistent hydration reaction intensity. Therefore, temperature control is unnecessary, greatly simplifying the steam curing process.

[0075] A comparison of Example 3 and Comparative Example 11 shows that when PVC directly impregnated with liquid nitrogen is ground and then added to aggregate, the performance improvement is not significant. This is because after grinding, the temperature of the PVC powder rises rapidly, making it easy for particles to agglomerate and difficult to disperse. This reduces the restraining effect on the aggregate when added to the curbstone, thus weakening the optimization effect.

[0076] As can be seen from Example 3 and Comparative Example 12, the performance of the prepared curbstone is low when a larger PVC cutting size is used. This indicates that when the initial cutting size is large, it is impossible to grind it into sufficiently fine particles in a short time. Furthermore, the increased temperature and flexibility of PVC during grinding make grinding difficult and lead to agglomeration, resulting in poor dispersibility in the curbstone.

Claims

1. A dry-hardened concrete curbstone, characterized in that, The dosage of each component in each cubic meter of dry-hard concrete curbstone is as follows: 350~400 kg of cement 30-70 kg of fly ash Iron tailings sand 850~900kg, 550-600 kg of 3-5 mm iron tailings. 5-8mm crushed stone 380-450kg, 70-85 kg of water 4-8 kg of polycarboxylate superplasticizer Modified PVC heat shrink film powder 0.5~1kg; The modified PVC heat shrink film powder is prepared by cutting PVC heat shrink film tailings into strip-shaped fragments with a width of no more than 2 mm and a length of no more than 4 mm, immersing them in liquid nitrogen, taking them out after full wetting, mixing them with iron tailings sand, and then rapidly ball milling them for 3 to 5 minutes under dry conditions to break them into powder with a particle size of no more than 50 μm, thus forming modified PVC heat shrink film powder. The method for preparing the dry-hardened concrete curbstone includes: (1) Mix the modified PVC heat shrink film powder, cement, fly ash, iron tailings sand, iron tailings ore and crushed stone evenly according to the above proportions to form solid material A; (2) Add the polycarboxylate superplasticizer and water to the solid material A above at the same time, stir evenly to form a mixed wet material B; (3) Pour the wet mixture B from step (2) into the mold, control the load to 10~12MPa, and press it into a curbstone blank; (4) Place the curbstone blank in a steam curing chamber for curing. There is no need for static curing or temperature setting. Place the blank directly in a curing chamber with the temperature controlled at 70~75℃ and steam for 6-12 hours. After the curing is completed, take it out and cure for 28 days to prepare dry hard concrete curbstone.

2. The dry-hardened concrete curbstone according to claim 1, characterized in that, In the preparation of the modified PVC heat shrink film powder, the mass fractions of PVC heat shrink film tailings and iron tailings sand are as follows: One portion of PVC heat shrink film waste. 50-200 parts of iron tailings sand.

3. A dry-hardened concrete curbstone according to claim 1 or 2, characterized in that, The thickness of the PVC heat shrink film tailings is 0.02~0.05mm.

4. A dry-hardened concrete curbstone according to claim 1, characterized in that, The cement is P.O42.5 ordinary Portland cement that conforms to the current national standard GB 175 "General Portland Cement"; The fly ash is Grade II or Grade I fly ash that meets the requirements of the current national standard GB / T 1596 "Fly Ash for Cement and Concrete". The crushed stone conforms to the relevant provisions of the current industry standard "Standard for Quality and Testing Methods of Sand and Stone for Ordinary Concrete" JGJ 52; The iron tailings sand is fine sand with a fineness modulus of 2.0~2.2 as specified in the current national standard "Iron Tailings Sand" GB / T 31288; The polycarboxylate superplasticizer is a superplasticizer that complies with the relevant provisions of the current industry standard "Carboxylic Acid-Based High-Performance Superplasticizers" JG / T 223.

Images