PCCP (prestressed concrete cylinder pipe) protective layer mortar indoor forming method

Abstract

The invention is applicable to the technical field of building materials, and provides a PCCP (prestressed concrete cylinder pipe) protective layer mortar indoor forming method which comprises the following steps: weighing cement, sand, water and a water reducing agent according to a mass ratio; firstly pouring the cement and the sand into a mortar mixer for mixing and stirring, and stirring at a low speed for 30 seconds to obtain a mixture; mixing a water reducing agent with water to prepare a mixed solution, slowly adding the mixed solution into the mixture, stirring at a low speed for 30 seconds, then stirring at a high speed for 30 seconds, stopping for 90 seconds, and then continuously stirring at a high speed for 60 seconds; the mixed mortar is added into the mold in two times, when the first layer is filled, the mortar with the height being 1 / 2 of that of each groove is put into each groove, and vibration is conducted for 60 times; and a second layer of mortar is loaded, the added mortar is slightly higher than the mold, vibration is performed again for 60 times, the mold is taken down from the compaction table, and the mold is leveled in the horizontal direction through a floating rule. The laboratory molding simulation method solves the problem of laboratory mix proportion optimization test caused by difficult molding of dry hard PCCP protective layer mortar, and is used for researching and improving the PCCP mortar performance.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials and relates to an indoor forming method of PCCP protective layer mortar. Background Art

[0002] In recent years, prestressed concrete cylinder pipe (PCCP) has been widely used in water supply trunk lines, urban sewage, agricultural irrigation, industrial water supply and other fields. PCCP pipelines are usually buried underground and are affected by environmental factors such as water quality and soil chemicals for a long time. The harsh service environment causes serious damage to the PCCP protective layer mortar. The mortar protective layer of the PCCP pipeline serves as the first line of defense to protect the PCCP structure. It can protect the prestressed steel wire of the pipeline from erosion and damage by the external environment, ensuring the safety and stability of the pipeline structure. If the corrosion resistance is insufficient, it will cause steel corrosion and concrete spalling, and eventually lead to pipeline failure, which may cause accidents such as pipe burst and leakage. Therefore, conducting a series of anti-corrosion test studies on the PCCP protective layer mortar has important theoretical significance and practical value.

[0003] Currently, two methods for producing PCCP protective layer mortar are roller spraying and shotcreting. Shotcreting is prone to dry dust pockets, cracking, and shedding, and the dust level in the working environment exceeds standards. The roller spraying method offers superior protective layer quality, economic efficiency, and environmental benefits. However, due to the large size, high cost, and complex process of roller spraying equipment, the on-site roller spraying method is not suitable for multiple mix optimization studies in the laboratory, and there is a lack of laboratory forming methods. PCCP protective layer mortar is a dry, hard mortar with a loose mortar structure and low cohesion. This makes it difficult to form using conventional indoor vibration forming methods, and the density cannot be guaranteed. Some researchers have used pressure forming methods in the laboratory, but this method is complex, inefficient, and prone to mold deformation, making it unsuitable for indoor batch production of PCCP mortar specimens. In summary, none of the above methods are suitable for indoor forming of PCCP mortar, making laboratory research on PCCP protective layer mortar difficult. Summary of the Invention

[0004] The purpose of the embodiments of the present invention is to provide a method for indoor forming of PCCP protective layer mortar, which aims to solve the problems raised in the above-mentioned background technology, so that when PCCP mortar specimens are prepared in the laboratory, the dry density, strength and water absorption rate of the mortar produced can meet the requirements of PCCP pipeline production standards, and it is also universal when different admixtures are added to study its various properties.

[0005] The embodiment of the present invention is implemented as follows: a method for indoor forming of PCCP protective layer mortar, comprising the following steps:

[0006] Step 1: Weigh cement, sand, water and water reducing agent according to mass ratio;

[0007] Step 2: Pour cement and sand into a mortar mixer and mix them. Stir at low speed for 30 seconds to obtain a mixture.

[0008] Step 3: Mix the water reducer with water to prepare a mixed solution, slowly add the mixed solution to the mixture, stir at a low speed of 145±5R / min for 30s, then stir at a high speed of 280±5R / min for 30s, stop for 90s, and then continue stirring at high speed for 60s;

[0009] Step 4: Add the mixed mortar into the mold in two batches. When installing the first layer, put about 300g (half the height of the groove) of mortar in each groove and vibrate 60 times; then add the second layer of mortar, adding mortar slightly higher than the mold, and vibrate 60 times. Remove the mold from the vibration table and smooth it horizontally with a scraper.

[0010] A further technical solution is that in step 1, ordinary Portland cement is selected as cement; natural sand is selected as sand, and the natural sand is fine sand with a fineness modulus of 2.2; the water reducer is a polycarboxylate water reducer, the solid content of the polycarboxylate water reducer is 23%, and the water reduction rate is 26%.

[0011] A further technical solution is that in step 1, 1 part of ordinary Portland cement, 2.4 parts of natural sand and fine sand, 0.3 part of water, and 0.01-0.04 part of polycarboxylate water reducer are taken.

[0012] A further technical solution is that in step 2, the time error of each stage should be controlled within ±1s.

[0013] A further technical solution is that in step 4, the mold is 70.7mm×70.7mm×70.7mm or 40mm×40mm×160mm or other sizes.

[0014] The present invention provides a method for indoor PCCP protective layer mortar molding, a laboratory molding simulation method for studying and improving PCCP mortar performance. This method simplifies molding steps and reduces costs, while ensuring that the performance of the PCCP protective layer mortar produced indoors is similar to that of actual roller-sprayed mortar in construction projects. This method does not require roller-spraying equipment, reducing site requirements and costs. It is highly efficient, can be molded in batches, and does not require cutting for strength testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The relationship between the demoulding density of the PCCP protective layer mortar and the water reducer dosage;

[0016] Figure 2The relationship between the compressive strength of PCCP protective layer mortar and the water reducing agent dosage;

[0017] Figure 3 This is the relationship between the water absorption rate of PCCP protective layer mortar and the water reducer dosage. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0020] An embodiment of the present invention provides a method for indoor forming of PCCP protective layer mortar, comprising the following steps:

[0021] Step 1: Weigh cement, sand, water and water reducing agent according to mass ratio.

[0022] Step 2: Pour cement and sand into a mortar mixer and mix them. Stir at low speed for 30 seconds to obtain a mixture.

[0023] Step 3: Mix the water reducer in water to prepare a mixed solution, slowly add the mixed solution into the mixture, stir at low speed (145±5R / min) for 30s, then stir at high speed (280±5R / min) for 30s, stop for 90s, and then continue stirring at high speed for 60s.

[0024] Step 4: Add the mixed mortar to the mold in two batches. When adding the first layer, place about 300g (half the height of the trough) of mortar in each groove and vibrate 60 times. Then add the second layer of mortar, adding mortar slightly higher than the mold, and vibrate 60 times again. Remove the mold from the vibrating table and smooth it horizontally with a scraper.

[0025] As a preferred embodiment of the present invention, ordinary Portland cement is selected as cement, which should comply with GB175-2023 "General Portland Cement".

[0026] The sand used should be natural sand, which should comply with GB / T14684-2022 "Construction Sand", and the natural sand should be fine sand with a fineness modulus of 2.2.

[0027] Water should comply with JGJ63-2006 "Standard for Water Use in Concrete".

[0028] The water reducer is a polycarboxylic acid water reducer with a solid content of 23% and a water reduction rate of 26%.

[0029] As a preferred embodiment of the present invention, in step 1, 1 part of ordinary Portland cement, 2.4 parts of natural sand and fine sand, 0.3 part of water, and 0.01-0.04 part of polycarboxylate water reducer are taken.

[0030] In the embodiment of the present invention, the specification stipulates the 28d compressive strength and 28d water absorption of PCCP mortar, and the 28d compressive strength and 28d water absorption of the prepared mortar are evaluated. The 28d compressive strength of the mortar is greater than 45MPa, and the 28d average water absorption of the mortar is less than 9%. It is considered that the mortar meets the requirements, indicating that the method is feasible.

[0031] As a preferred embodiment of the present invention, in step 2, the time error of each stage should be controlled within ±1s.

[0032] As a preferred embodiment of the present invention, in step 4, the mold is 70.7 mm×70.7 mm×70.7 mm or 40 mm×40 mm×160 mm or other sizes.

[0033] Several specific examples are provided below to verify the effectiveness of this method.

[0034] The cement used was Tianshan P·O 42.5R cement. The sand was natural, fine sand (fineness modulus 2.2, mud content 0.8%). The water reducer was a polycarboxylate water reducer with a water reduction rate of 26% and a solid content of 23%.

[0035] The components and mix ratios (mass percentages) of the mortars in Examples 1-7 are shown in Table 1 below.

[0036] Table 1

[0037] cement water sand water reducer Example 1 1 0.3 2.6 0.01 Example 2 1 0.3 2.6 0.015 Example 3 1 0.3 2.6 0.02 Example 4 1 0.3 2.6 0.025 Example 5 1 0.3 2.6 0.03 Example 6 1 0.3 2.6 0.035 Example 7 1 0.3 2.6 0.04

[0038] In Examples 1-3, the preparation method of the mortar molding specimens of each example is as follows:

[0039] Step 1: Molding process;

[0040] Mix the weighed cement and sand according to the component ratio and place them in a blender. Add the weighed water reducer to the water and set aside. Immediately start the mixer and stir at low speed for 30 seconds. Then slowly add the water (including the water reducer). Stir again at low speed (145±5 rpm) for 30 seconds, then at high speed (280±5 rpm) for 30 seconds, pausing for 90 seconds; then continue stirring at high speed for 60 seconds. The time error for each stage should be within ±1s. Add the freshly mixed mortar to the mold in two batches. For the first layer, place approximately 300g of mortar in each groove and manually insert and tamp 60 times. Then add the second layer of mortar, adding mortar slightly above the mold, insert and tamp 60 times again, and smooth horizontally with a scraper. Mark with paper and leave indoors for 24 hours.

[0041] Step 2: Maintenance;

[0042] The molded specimens were covered with plastic film and allowed to rest for 24 hours at room temperature. After 24 hours, the molds were removed and the specimens were placed in a standard curing room for curing.

[0043] In Examples 4-7, the preparation method of the mortar molding specimens of each example is as follows:

[0044] Step 1: Molding process;

[0045] Mix the weighed cement and sand according to the component ratio and place them in a blender. Add the weighed water reducer to the water and set aside. Immediately start the blender and stir at low speed for 30 seconds. Then, slowly add the water (including the water reducer). Stir again at low speed (145±5 rpm) for 30 seconds, then at high speed (280±5 rpm) for 30 seconds, pausing for 90 seconds; then continue stirring at high speed for 60 seconds. The time tolerance for each stage should be within ±1s. Secure the mold on a vibrating table and add the freshly mixed mortar to the mold in two batches. For the first layer, place approximately 300g of mortar in each trough and vibrate 60 times. Then, add the second layer of mortar, adding mortar slightly above the mold. Vibrate 60 times again. Remove the mold sleeve, remove the mold from the vibrating table, and smooth the surface horizontally with a scraper. Mark with a paper strip and store indoors for 24 hours.

[0046] Step 2: Maintenance;

[0047] The vibrated specimens were covered with plastic film and allowed to rest at room temperature for 24 hours. After 24 hours, the molds were removed and the specimens were placed in a standard curing room for curing.

[0048] The specimens of Examples 1-7 were cured for 7 and 28 days, respectively, and then subjected to compressive strength tests. The test results of the demoulding density, compressive strength, and water absorption properties of the prepared mortars of Examples 1-7 with different water-reducing agent dosages are shown in Table 2.

[0049] Table 2

[0050]

[0051] like Figure 1-Figure 3 As shown ( Figure 1 The five-pointed star in the middle represents the demolding density of the mortar corresponding to the corresponding water-reducing agent dosage). The demolding density and compressive strength of the mortar increase with the increase of the water-reducing agent dosage. The average water absorption at 7d and 28d decreases first and then increases with the increase of the water-reducing agent dosage. When the water-reducing agent dosage is 3%, the average water absorption of the mortar is the lowest. At the same time, when the water-reducing agent dosage is 3% to 4%, the 28d compressive strength of the mortar meets the requirements of the specification. When the water-reducing agent dosage is 2.5% to 4%, the 28d average water absorption of the mortar meets the requirements of the specification. According to the test results, the optimal water-reducing agent dosage for PCCP mortar indoor tests is 3%. At this time, the demolding density of the mortar is 2249.05kg / m 3 .

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A PCCP protective layer mortar indoor forming method, characterized in that: The following steps are involved: Step 1: Weigh cement, sand, water and water reducing agent according to mass ratio; Step 2: Pour cement and sand into a mortar mixer and mix them. Stir at low speed for 30 seconds to obtain a mixture. Step 3: Mix the water reducer with water to prepare a mixed solution, slowly add the mixed solution to the mixture, stir at a low speed of 145±5R / min for 30s, then stir at a high speed of 280±5R / min for 30s, stop for 90s, and then continue stirring at high speed for 60s; Step 4: Add the mixed mortar into the mold in two batches. When installing the first layer, put 1 / 2 slot high mortar in each slot and vibrate 60 times. Then add the second layer of mortar, adding mortar slightly higher than the mold, and vibrate 60 times. Remove the mold from the compaction table and smooth it horizontally with a scraper.

2. The PCCP protective layer mortar indoor forming method according to claim 1 is characterized in that: In step 1, ordinary Portland cement is selected as cement; natural sand is selected as sand, and the natural sand is fine sand with a fineness modulus of 2.2; the water reducer is a polycarboxylate water reducer, and the solid content of the polycarboxylate water reducer is 23% and the water reduction rate is 26%.

3. The indoor forming method of PCCP protective layer mortar according to claim 2 is characterized in that: In step 1, take 1 part of ordinary Portland cement, 2.4 parts of natural sand and fine sand, 0.3 parts of water, and 0.01-0.04 parts of polycarboxylate water reducer.

4. The PCCP protective layer mortar indoor forming method according to claim 1, characterized in that: In step 2, the time error of each stage should be controlled within ±1s.

5. The PCCP protective layer mortar indoor forming method according to claim 1 is characterized in that: In step 4, the size of the mold is 70.7 mm×70.7 mm×70.7 mm or 40 mm×40 mm×160 mm.

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