A method of finishing a roller compacted concrete layer

Abstract

The application discloses a roller compacted concrete layer surface treatment method, comprising the following steps: detecting the layer surface hardness and hydration degree of the lower layer of the roller compacted concrete; when the layer surface hardness is greater than 5 mm and the hydration degree is less than 0.8, the layer surface treatment mode adopts inserting and tamping and water spraying; when the layer surface hardness is not greater than 5 mm and the hydration degree is not less than 0.8, the layer surface treatment mode adopts brushing, water spraying after cleaning and laying an intermediate cushion mixture. The application proposes a specific and accurate lower layer construction surface state control method and evaluation index in view of the lack of scientificity and accuracy of the current roller compacted concrete lower layer construction surface state evaluation index and the complexity of the on-site construction condition, improves the layer surface bonding strength, stability and durability and the like, and solves the problems of poor scientificity, accuracy, economy and effectiveness of the current roller compacted concrete layer surface treatment method.

Description

Technical Field

[0001] This invention relates to the field of roller-compacted concrete, and in particular to a method for treating roller-compacted concrete surfaces. Background Technology

[0002] Roller-compacted concrete (RCC) dams are a new type of dam that emerged in the dam construction industry seeking a fast and economical way to build concrete gravity dams. Due to their low cost and rapid construction, this type of dam has gained worldwide recognition in a short period. However, due to the dry-hard nature of the RCC mix and the characteristics of layered compaction, a large number of poorly bonded horizontal layers exist, which have a significant impact on the safe operation of the dam.

[0003] Research and practical engineering show that layers poured continuously within a certain time do not require special treatment; however, when the construction interval between two layers of concrete exceeds the allowable value and the lower joint surface has reached the cold joint state, appropriate layer treatment is required. Conventional methods require first removing the lower layer of laitance and loose aggregate, and then laying a layer of neat cement paste, mortar, or concrete to increase the interlayer bonding capacity; existing layer treatment methods are simple, convenient, and quick to implement. However, existing surface treatment methods that allow direct paving or require the application of mortar or other subbase mixtures primarily rely on concrete setting time as the determining factor. The condition of the underlying concrete surface, which directly determines the bonding capacity of the surface, is also influenced by environmental factors such as temperature, humidity, and wind speed at the construction site. Currently, there is a lack of scientifically sound and accurate evaluation indicators for the surface condition. Furthermore, given this lack of evaluation indicators, the specific type, properties, thickness, and method of the subbase mixture must be determined based on experience. Coupled with changes in on-site construction plans, rainfall, or other factors, entirely new requirements are needed for surface condition evaluation indicators, subbase mixtures, and their application methods. Therefore, a new type of roller-compacted concrete surface treatment method is urgently needed.

[0004] Existing technologies include methods for detecting the degree of hydration and permeability coefficient of the sublayer in roller-compacted concrete. Current standards primarily determine the degree of concrete hydration through setting time, but there is also extensive research on external factors influencing cement hydration. The most widely accepted method for determining the degree of cement hydration is the hydration degree method. This invention optimizes the hydration degree formula based on research findings. t0 is the initial setting time of the concrete, V is the average wind speed at the measurement site, t is the time it takes for the concrete layer to be completed at the measurement site, H is the humidity at the measurement site, and T is the average temperature at the measurement site. The permeability coefficient can be measured according to the DLT 5150-2017 Test Procedure for Hydraulic Concrete. Test methods for determining the permeability coefficient of concrete include the DLT5150-2017 water pressure test method, chloride permeability test method, and gas permeability test method. The water pressure test method is simpler than the latter two methods. The gas permeability test method is more suitable for on-site testing, but its application is relatively limited in my country; laboratory testing mainly uses the first two methods. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for treating roller-compacted concrete layers to improve the bonding strength, stability and durability of the layers, in order to address the shortcomings of the existing technology.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for treating roller-compacted concrete surfaces, comprising the following steps:

[0007] Test the surface hardness and hydration degree of the underlying layer of roller-compacted concrete;

[0008] When the surface hardness is greater than 5 mm and the hydration degree is less than 0.8, the surface treatment method is to tamp and sprinkle water.

[0009] When the surface hardness is not greater than 5mm and the hydration degree is less than 0.8, the surface treatment method is to brush and clean it, then sprinkle water, and then lay the intermediate bedding layer mixture, which is mortar.

[0010] The surface hardness was determined using the falling ball method, recording the depth of the ball drop.

[0011] Concrete hydration is affected by on-site temperature, humidity, and wind speed. The higher the temperature, the lower the humidity, and the faster the wind speed, the lower the degree of hydration and the smaller the degree of hydration θ. When θ is less than 0.8, the hydration degree of the paste in roller-compacted concrete is relatively low, and it can be better bonded to the next layer of roller-compacted concrete after tamping and sprinkling.

[0012] After brushing and cleaning, the surface should have a slight exposure of coarse sand without any loose slurry or aggregate. The permeability coefficient characterizes the number and size of capillary pores and surface gaps in the interlayer, and has a significant impact on the slurry properties of the intermediate bedding layer and the selection of the sand fineness modulus.

[0013] The surface hardness is determined using the falling ball method, which involves dropping a steel ball with a diameter of 20-30mm from a distance of 0.2-0.8m from the surface and recording the depth of the drop.

[0014] In a preferred embodiment of the invention, the roughness and permeability coefficient of the roller-compacted concrete sublayer are tested before the intermediate sublayer mixture is laid.

[0015] When hydration degree ≥ 0.9, roughness ≤ 0.02, and permeability coefficient ≤ 5.0 × 10⁻⁶. -8 The cement fineness of the cement slurry in the intermediate bedding layer mixture is controlled at 270-300 μm / h. 2 / kg, and the 3-day hydration heat value of cement is less than 250kJ / kg;

[0016] When the following conditions are not met: hydration degree ≥ 0.9, roughness ≤ 0.02, and permeability coefficient ≤ 5.0 × 10⁻⁶ -8 When the flow rate is cm / h, the cement fineness of the cement paste in the intermediate cushion layer mixture is 300-330 μm. 2 / kg;

[0017] The roughness testing method involves cleaning and drying the surface layer of the roller-compacted concrete, taking 500ml of fine powder into a cylinder, inverting the cylinder onto the surface layer, spreading and smoothing the fine powder to form a disc shape, and measuring the average diameter D of the disc.

[0018] The intermediate cushion layer mixture is mortar, and the ratio of cement paste, sand and mortar is selected according to the degree of hydration, roughness and permeability.

[0019] The fineness of the cement paste should be controlled between 270-330 μm. 2 / kg, the higher the degree of hydration, the lower the roughness, and the lower the permeability coefficient, the lower it should be between 270-330m. 2 Within the range of / kg, a smaller cement fineness should be selected to ensure that cement particles fully enter the interlayer gaps. However, considering the issues of cost and heat generation leading to excessively rapid and insufficient cement hydration, it is necessary to avoid excessively fine fineness and control the 3d hydration heat value of cement to be less than 250kJ / kg.

[0020] The coarseness of the fine powder can be selected from dry cement, fly ash, mineral powder, etc., depending on the on-site material conditions, and the fineness must be less than 250 μm. 2 / kg.

[0021] In a preferred embodiment of the present invention, after the brush bristles are cleaned and then sprayed with water, 0.06-0.08 wt% of an active agent is added to the water, wherein the active agent is selected from one or two of hydroxycarboxylic acids, aminocarboxylic acids and polycarboxylic acids.

[0022] The activator promotes the hydration of cement particles in the mortar at the surface layer, thereby increasing the bond strength. The activator also promotes the formation of CSH gel, enhancing the adsorption of cement particles in the intermediate layer, the strength of the hardened material at the bond joint, and the structural density, thus increasing the mortar bond strength.

[0023] In a preferred embodiment of the present invention, the sand in the intermediate cushion layer mixture is natural sand or manufactured sand, and the fineness modulus is controlled at 2.2-2.5.

[0024] The sand should be natural or manufactured, with a fineness modulus controlled between 2.2 and 2.5. It is necessary to prevent the sand particles from being too fine, which would cause severe water absorption and affect cement hydration, and also to prevent the sand particles from being too coarse, which would cause the mortar to contain air and have too many gaps, affecting its strength and bonding.

[0025] In a preferred embodiment of the present invention, the saturated water absorption rate of the sand is 0.5%-1.0%, and 0.05%-0.06% of defoamer is added to the mortar.

[0026] The saturated water absorption rate of sand should be controlled at 0.5%-1.0%. 0.05%-0.06% of defoamer can be added to the mortar. When the roughness is small, the fineness modulus can be increased accordingly within 0.5%-1.0% to increase the mortar's binding properties.

[0027] In a preferred embodiment of the present invention, the volume of water sprayed after brushing and cleaning is 80-120 ml / m³. 2 .

[0028] The water spraying rate is adjusted between 80-120 ml / m based on the surface roughness and permeability coefficient. 2 Within this range, the greater the roughness and permeability coefficient, the corresponding water spraying volume is 80-120 ml / m². 2 Choose the larger value within the range.

[0029] In a preferred embodiment of the present invention, the intermediate cushion layer mixture comprises 10-30% fly ash.

[0030] The intermediate layer mixture includes 10-30% fly ash to reduce calorific value, ensuring full hydration of cement particles, increasing bond strength, and enhancing the durability of the intermediate layer.

[0031] In a preferred embodiment of the present invention, the intermediate cushion layer mixture includes 0.4%-0.6% of a retarding high-efficiency water-reducing agent.

[0032] Adding 0.4%-0.6% of a retarding high-efficiency water-reducing agent to cement slurry can improve the hydration degree of cement particles, the adsorption effect, and reduce the gaps between particles, thereby improving the bonding strength with the surface layer.

[0033] In a preferred embodiment of the present invention, the mortar ratio of the intermediate cushion layer mixture is 0.3-0.4.

[0034] The higher the degree of hydration and the lower the permeability coefficient, the more the mortar-cement ratio needs to be increased to ensure sufficient slurry. Excessive roughness can easily form gaps between the layer and the mortar, while too little roughness can lead to interlayer air bubbles. Both require an appropriate increase in the mortar-cement ratio. However, an excessively high mortar-cement ratio can also lead to a decrease in the strength of the intermediate layer and an increase in raw material and construction costs.

[0035] In a preferred embodiment of the present invention, the degree of hydration Where K ranges from 0.1 to 0.15, t0 is the initial setting time of the concrete, V is the average wind speed at the measurement site, t is the completion time of the layer at the measurement site, H is the humidity at the measurement site, and T is the average temperature at the measurement site. When K ranges from 0.1 to 0.15, the measured degree of hydration is the degree of hydration of the roller-compacted concrete layer.

[0036] In a preferred embodiment of the present invention, the thickness of the intermediate cushion layer mixture is greater than 20 mm.

[0037] As the strength and surface roughness of roller-compacted concrete increase, or the fineness of mortar cement and the fineness modulus of sand decrease, the thickness of the intermediate bedding layer mixture needs to be appropriately increased.

[0038] The tamping rod used should have a diameter of 0.1-0.2m and a tamping depth of 0.4-0.8m. The greater the hardness, the smaller the diameter and depth should be. After tamping, ordinary tap water should be used, with the water volume controlled at 50-100ml / m. 2 .

[0039] This invention addresses the lack of scientific rigor and accuracy in current evaluation indicators for the condition of the lower layer of roller-compacted concrete (RCC), the lack of clarity regarding the type, properties, and thickness of the intermediate bedding layer mixture, and the complexity of on-site construction conditions. It proposes specific and accurate methods and evaluation indicators for controlling the condition of the lower layer. Furthermore, it clarifies the type, properties, and thickness of the corresponding bedding layer mixture, improving the bonding strength, stability, and durability of the layers. This solves the problems of poor scientific rigor, accuracy, economy, and effectiveness in current RCC surface treatment methods.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] (1) The evaluation indicators of the layer are more comprehensive, scientific and reasonable: the concrete setting condition is evaluated by strength and hydration degree, and the influence of environmental factors such as temperature, humidity and wind speed on cement hydration is comprehensively considered. Based on this, the chemical bonding force that cement can provide is judged. At the same time, the physical interlocking force and adsorption force of hydration products that aggregate can provide are judged by the surface roughness and porosity. It is more comprehensive, scientific and reasonable than the traditional setting time evaluation indicators.

[0042] (2) Improve construction efficiency and save costs: For different surface conditions, reasonable and specific surface treatment methods are proposed, which reduces the process of manual experience judgment, avoids subjective errors, and improves construction efficiency; the performance state and thickness of mortar are precisely controlled to give full play to its bonding effect, improve material utilization and save costs.

[0043] (3) Improve the performance of the layer, enhance safety and economic benefits: The layer treatment method of the present invention can significantly improve the bonding strength of the roller-compacted concrete layer, and also improve the durability of the interlayer structure such as impermeability and frost resistance, and greatly extend the design service life. It has significant safety and economic benefits and is suitable for widespread application. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the layer processing method in Embodiment 2 of the present invention. Detailed Implementation

[0045] like Figure 1 As shown below, the present invention will be further described in detail with reference to specific embodiments. However, the implementation of the present invention is not limited to the scope shown in the embodiments. These embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0046] Example 1

[0047] A method for treating roller-compacted concrete surfaces is as follows: Based on the hardness and hydration degree testing methods of this invention, the surface hardness is 6 mm, the temperature is 30℃, the humidity is 50%, the average wind speed is 10 m / s, the surface completion time is 30 min, the initial setting time is 1 h, and the hydration degree is 0.7. Therefore, the method of tamping and watering is directly adopted. The tamping rod has a diameter of 0.14 m and a tamping depth of 0.5 m. After tamping, ordinary tap water is used, and the watering volume is controlled at 60 ml / m. 2 After watering, the next layer of roller-compacted concrete was laid directly. Standard specimens were formed according to the above-mentioned layer treatment method, and the compressive strength, axial tensile strength and impermeability of the concrete specimens were tested according to the specifications. The test results are as follows.

[0048] Table 1. Performance test results of roller-compacted concrete pavement.

[0049]

[0050] Example 2

[0051] A method for treating roller-compacted concrete surfaces is as follows: First, the surface hardness is measured to be 4.5 mm, temperature 30℃, humidity 50%, average wind speed 10 m / s, surface completion time 40 min, initial setting time 1 h, and hydration degree 0.93; after cleaning and drying the underlying surface, a 200 μm fineness test is performed. 2 / kg of fly ash yielded a roughness of 0.016; further, the permeability coefficient was measured to be 4.9×10⁻⁶ according to specifications. -8 cm / h, after brushing and cleaning, slightly exposed coarse sand with no floating slurry or loose aggregate; after brushing and cleaning, water is sprayed with 0.07wt% polycarboxylate activator added to the water, and the spraying volume is 100ml / m. 2The intermediate subbase mixture is mortar, with cement fineness of 280 μm. 2 / kg, 3d hydration calorific value 220kJ / kg, 20% fly ash and 0.5% retarding high-efficiency water-reducing agent added to the cement paste; the sand is manufactured sand with a fineness modulus of 2.3 and a saturated water absorption rate controlled at 0.8%, and 0.06% defoamer can be added to the mortar; the mortar thickness is 30mm; standard specimens are formed according to the above-mentioned surface treatment method, and according to

[0052] The DL T 5150-2017 Test Procedure for Hydraulic Concrete was used to test the compressive strength, axial tensile strength, and impermeability of concrete specimens. The test results are as follows.

[0053] Table 2. Performance test results of roller-compacted concrete pavement.

[0054]

[0055] Example 3

[0056] The DLT5112-2009 "Specification for Construction of Roller-Compacted Concrete in Hydraulic Engineering" and the "Specification for Construction of Hydraulic Concrete" stipulate that no special treatment is required for layers poured continuously within the allowable time. If the interval between two layers exceeds the allowable value and the joint surface has reached a cold joint state, then appropriate layer treatment is required.

[0057] The difference from Example 2 is that, according to the initial setting time method specified in DLT5112-2009 "Specification for Construction of Roller-Compacted Concrete in Hydraulic Engineering" and "Specification for Construction of Hydraulic Concrete", the next layer of roller-compacted concrete was laid directly without surface treatment measures and mortar laying. The compressive strength, axial tensile strength and impermeability of the concrete specimens were tested, and the test results are as follows.

[0058] Table 3. Performance test results of roller-compacted concrete pavement.

[0059]

[0060] The comparison shows that determining whether to lay mortar or proceed directly to the next layer of roller-compacted concrete based on setting time is greatly affected by the environment, and improper handling can easily lead to serious loss of the layer's performance.

[0061] Example 4

[0062] The difference from Example 2 is that the fineness of the mortar cement is 350 μm. 2 / kg, and everything else was the same as in Example 2. The compressive strength, axial tensile strength, and impermeability of the concrete specimens were tested, and the results are as follows.

[0063] Table 4. Performance test results of roller-compacted concrete pavement.

[0064]

[0065]

[0066] The comparison shows that excessively fine cement cannot ensure that cement particles fully enter the gaps between the layers, resulting in poor adhesion between the mortar and the layer and a decline in the performance of the layer.

[0067] Example 5

[0068] The difference from Example 2 is that tap water was used for brushing and cleaning without the addition of surfactants; otherwise, it was the same as Example 2. The compressive strength, axial tensile strength, and impermeability of the concrete specimens were tested, and the results are as follows.

[0069] Table 5. Performance test results of roller-compacted concrete pavement.

[0070]

[0071] The comparison shows that the addition of activator promotes the hydration of cement particles in the mortar at the surface, thereby increasing the bonding strength and surface durability.

[0072] Example 6

[0073] The difference from Example 2 is that no defoamer was added; all other aspects are the same as in Example 2. The compressive strength, axial tensile strength, and impermeability of the concrete specimens were tested, and the results are as follows.

[0074] Table 6. Performance test results of roller-compacted concrete pavement.

[0075]

[0076] The comparison shows that the addition of defoamer reduces the air content and gaps in the mortar, thereby increasing the bonding strength and surface durability.

Claims

1. A method of treating a roller compacted concrete surface, characterized by The method comprises the following steps: detecting the layer hardness and hydration degree of the roller compacted concrete lower layer; when the layer hardness is greater than 5 mm and the hydration degree is less than 0.8, the roller compacted concrete lower layer is treated by inserting and tamping and spraying water; when the layer hardness is not greater than 5 mm and the hydration degree is not less than 0.8, the roller compacted concrete lower layer is treated by brushing, spraying water after cleaning, and then laying the intermediate cushion mixture, wherein the intermediate cushion mixture is mortar; the layer hardness is detected by the falling ball method, and the ball falling depth is recorded; the roughness and permeability coefficient of the roller compacted concrete lower layer are detected before laying the intermediate cushion mixture; When hydration degree ≥ 0.9, roughness ≤ 0.02, and permeability coefficient ≤ 5.0 × 10⁻⁶. -8 The cement fineness of the cement slurry in the intermediate bedding layer mixture is controlled at 270-300 μm / h. 2 / kg, and the 3-day hydration heat value of cement is less than 250kJ / kg; When the water-cement ratio is not satisfied with the condition of water-cement ratio ≥ 0.9 and roughness ≤ 0.02 and permeability coefficient ≤ 5.0 × 10 -8 cm / h, the cement paste cement fineness of the intermediate cushion mixture is 300-330 m 2 / kg. The method for detecting roughness includes taking 500 ml fine powder in a cylinder after the layer surface of the roller compacted concrete lower layer is cleaned and dried, inverting the cylinder on the layer surface to spread and flatten the fine powder to form a round cake, measuring the average diameter D of the round cake, and calculating the roughness R according to the following formula: R = D - 2h, wherein h is the thickness of the fine powder layer. ; Degree of hydration where K ranges from 0.1 to 0.15, t0 is the initial set time of the concrete, V is the average wind speed at the measurement site, t is the time of completion of the layer at the measurement site, H is the humidity at the measurement site, and T is the average temperature at the measurement site.

2. The roller compacted concrete pavement treatment method according to claim 1, wherein: after brushing and spraying water after cleaning, 0.06-0.08 wt% of an active agent is added into the water, wherein the active agent is selected from one or two of a hydroxyl carboxylic acid, an amino carboxylic acid and a polycarboxylic acid.

3. The roller compacted concrete pavement treatment method of claim 1, wherein: the sand in the intermediate cushion mixture is natural sand or machine-made sand, and the fineness modulus is controlled to be 2.2-2.

5.

4. The roller compacted concrete pavement treatment method according to claim 3, wherein: the saturated water absorption rate of the sand is 0.5%-1.0%, and 0.05%-0.06% of a defoaming agent is added into the mortar.

5. The roller compacted concrete surface treatment method according to any one of claims 2-4, wherein: The volume of water for post-cleaning sprinkling is 80-120 ml / m 2 .

6. The roller compacted concrete surface treatment method according to any one of claims 2-4, wherein: 10-30% of fly ash is included in the intermediate cushion mixture.

7. The roller compacted concrete surface treatment method according to any one of claims 2-4, wherein: 0.4%-0.6% of a retarder type high efficiency water reducing agent is included in the intermediate cushion mixture.

8. The roller compacted concrete surface treatment method according to any one of claims 2-4, wherein: the cement-sand ratio of the intermediate cushion mixture is 0.3-0.4.

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