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Talk about the quality control of wet mixed mortar
Update time：2017-09-08 00:36:14clicks：2027次Type size：T|T
Abstract: Wet mixed mortar is composed of cement, fine aggregate, admixtures, admixtures, additives and water. This paper mainly introduces the common problems or knowledge sharing in the production of wet mixed mortar from different raw materials one by one, and expounds the quality control methods and lessons in the production of wet mixed mortar combined with actual case analysis.
Key words: wet mixed mortar quality fluctuation case analysis
1 Introduction
In 2016, the Central Committee of the Communist Party of China and The State Council issued Several Opinions on Further Strengthening the Management of Urban Planning and Construction, which made special instructions on improving the evaluation system of green energy-saving buildings and building materials and promoting green buildings and building materials. Wet mixed mortar is a green building material widely used in housing construction and municipal engineering, and its environmental protection and energy saving function is increasingly prominent, which is an important aspect of the green transformation and development of the construction industry. From January to June 2016, the country produced a total of 35.1291 million tons of ready-mixed mortar, an increase of 4.715 million tons last year, an increase of 15.5%. Among them, wet mixed mortar: During the same period, the national output of wet mixed mortar totaled 4,661,800 cubic meters, an increase of 1,483,100 cubic meters from last year's 3,178,700 cubic meters, an increase of 46.66%. Wet mixed mortar accounted for 21.23% of the total production of ready-mixed mortar in China. As the industry gradually recognizes the advantages of wet mixed mortar in environmental protection, its development trend is obvious. However, wet-mixed mortar continues to develop steadily, requiring more industry people to constantly ask questions and sum up experience.
2 Common problems in wet mixed mortar production
Wet mixed mortar is cement, fine aggregate, mineral admixtures, admixtures, additives and water, according to a certain proportion, in the mixing station, after the measurement, mixing, sent to the use of the site, and used within the specified time of the mix. The common quality problems of wet mixed mortar are mainly related to the quality fluctuation of raw materials, the rationality of mix ratio design, production control, technical personnel production and quality control and environment. Based on the practical cases of quality problems of wet mixed mortar for many years, this paper summarizes some common problems in production for reference and guidance of relevant practitioners.
2.1 Fluctuation of cement quality
From the perspective of the influence of raw materials, cement is a relatively small probability of problems, but there are still cement quality fluctuations in the actual mortar quality cases every year that affect the performance stability of wet mixed mortar. The fluctuation of cement quality usually affects the consistency loss of mortar, viscosity and other construction performance, which shows that the mortar dries out after a few hours on the site, the viscosity becomes worse, and a lot of water is needed to carry out construction, and even the mortar hardens for a few hours.
2.1.1 Case analysis
The mortar of a mixing station has been continuously complained at the site, the mortar is loose, the viscosity is not high, the wall cannot be hung, the sand sense is coarse, and the mortar left in the station is black in color, not bright, astringent, and hardened in advance.
Through the experiment, it is found that the mortar state and performance of different brands of cement are very different. The preliminary conclusion is that the clinker and admixture of the cement brand used in the current production are different from those used in the previous production, which affects the mortar state and performance. In the evening, the production mortar was changed to the previous brand cement, according to the original mix ratio, the next morning the site to check the mortar situation, the workers responded that the mortar was easy to use, the workability was good, and there were no site complaints during the day.
Therefore, the cement brand replacement of wet mixed mortar and the switch of different batches must be done to confirm the performance and status of mortar. If there is an anomaly, it must be adjusted in time to ensure that the performance and state of the mortar meet the requirements of the standards and actual site construction.
2.2 Fly ash quality fluctuation
Fly ash is the waste residue discharged from coal-fired power plants. During the combustion of pulverized coal suspended at high temperature, the clay minerals contained in pulverized coal melt and form liquid drops. The chemical composition of pulverized coal fly ash fluctuates widely in different discharge types, fineness of pulverized coal and combustion conditions. Then, after rapid cooling, it becomes a fine spherical particle with a particle size of 1-50 microns. First of all, due to the rough surface of the irregular porous glass body of coal and fly ash, there are many water storage cavities, and the water demand increases, which reduces the activity of fly ash. In addition, the unburned carbon in fly ash is harmful to its quality. When the fly ash with high carbon content is mixed into cement, the water demand often increases and the strength is greatly reduced. In addition, when the unburned carbon meets water, a water-phobic film can be formed on the surface of the particles, preventing the infiltration of water into the fly ash particles, thus affecting the interaction between the cement hydration product Ca(0H)2 and the active oxide, and reducing the activity of the fly ash.
The experimental analysis conclusion in the paper "Study on the Effect of fly ash Quality on the performance of plaster-mortar" also mentioned that (1) After 25% cement is replaced by grade Ⅲ raw ash and ground grade Ⅱ ash, the water consumption of mortar increases, the water retention rate decreases, the working ability decreases, the consistency loss increases, the shrinkage rate increases, and the compressive strength and bond strength are greatly lost, which not only reduces the construction efficiency, but also reduces the construction efficiency. It is also very easy to cause the hollow drum cracking in the later stage of plastering mortar, so it is recommended to use cautiously or not in production. If one of the two must be chosen, the first choice should be ground grade II ash. (2) The addition of grade I fly ash and grade II fly ash can improve the workability of mortar, increase the water retention rate of mortar, reduce the consistency loss and shrinkage rate of mortar, and the loss of compressive strength is small; The later strength of the mortar mixed with grade I fly ash can even exceed that of the mortar replaced before, which can improve the construction efficiency to a certain extent and reduce the risk of mortar hollow drum cracking, so it is recommended to be preferred in production.
The quality fluctuation of admixture fly ash is the key factor affecting the performance of wet mixed mortar. The selection of fly ash quality affects the increase of mortar water consumption, the decrease of water retention rate, the deterioration of workability and the increase of consistency loss. In fact, the mixing of fly ash quality control is still insufficient, often ignored in the production of mortar test between batches of confirmation, until the site problems to pay attention to it. Fly ash quality fluctuations lead to mortar quality complaints in the site is more common, mixing station need to do several groups of fly ash mortar with different content test to adjust the production mix ratio.
2.3 Sand gradation and fineness modulus change
Sand is used as the aggregate of the mortar and plays the main role of aggregate filling in the mortar. Natural sand with fineness modulus of 2.3-2.7 should be preferred for fine aggregates used in the production of wet mixed mortar. If the machine-made sand is selected, whether there is a defect in its particle grading is considered, and fine aggregates with different fineness modules are required to be used together to obtain the mortar with appropriate particle grading. The content of fine aggregate has a great influence on the volume stability of mortar, and the volume shrinkage of mortar with a large content of fine aggregate is relatively small, and the probability of plastic cracks in mortar is correspondingly reduced. Therefore, the impact of sand gradation and fineness modulus changes can be improved by optimizing or matching sand, or by appropriately optimizing the overall mix ratio of mortar to make up for the impact of its deficiency.
2.3.1 Case analysis
The gradation of mortar reaction sand in a mixing plant becomes worse and the fineness modulus becomes larger, and the mortar cannot be in a good state according to the original matching ratio. Through on-site adjustment and optimization of the mix ratio, the appropriate increase of water reducing agent can improve the coating property of mortar and the uniform distribution of slurry, and the reasonable fusion of slurry and aggregate in the mortar system can be improved, and the state of mortar can meet the standards and site requirements.
Of course, the mud content of the sand also has a great impact on the mortar. The mud content of sand is recommended to be controlled below 3%, but the mud content in some areas often exceeds 3%. Then, the mortar production process needs to pay careful attention to the change of mud content, if beyond the control of the original mix system, the mortar sent to the site may have problems, such as the mortar opening time is shortened, the mortar shrinkage cracking and so on. Therefore, the mud content is beyond the control range of the original mortar mix ratio system, and the mortar mix ratio must be readjusted and optimized through experiments.
2.4 Rational utilization of circulating water
The waste water produced by concrete mixing station contains cement slurry, admixtures, aggregates and other alkaline substances, direct discharge will seriously pollute the environment, and the transportation with clean water has caused a huge waste. For this reason, many mixing stations now recycle waste water, and some mixing stations begin to use circulating water to produce mortar. At present, the use of circulating water to produce wet mixed mortar needs to be cautious, if the proportion of wastewater utilization is not well mastered, the mortar is prone to abnormalities.
2.4.1 Case analysis
The mortar produced by a mixing station at 10 o 'clock at night has a very small consistency to the site, and the tank car cannot discharge the material. The situation is investigated at the station, and the mortar returned from the mortar tank car is checked. The mortar loss is indeed very serious and the mortar status is very serious. The mortar can recover the construction performance by adding water reducing agent to blend the returned mortar. Next, the production mix, equipment, materials are checked, and the trial is carried out at the same time, no abnormal mortar was found, the equipment scale is no problem, the mix is no problem, no abnormal link was found, and then the production is carried out according to the original steps, with the car to the site, the mortar is normal. This happened again the next night, and the mortar returned to normal after a few carloads of production. On the third night of production, the water source is replaced for production, and the occasional loss of mortar consistency on the site is completely resolved.
The main reason for the mortar problems in the station is that the concentration of waste water in the storage pool is too high, there is production of concrete, and there is carboxylic acid in the waste water, which has a negative effect on the mortar admixture and affects its normal function and effect. Therefore, the production of mortar water should pay attention to the proportion of waste water. Because most mixing plants produce concrete and mortar at the same time, the impurities contained in the recovered wastewater are complex, and the high concentration of wastewater during production is bound to affect the consistency loss and slump loss of mortar or concrete.
2.5 Stability and adaptability of admixtures
In recent years, wet-mixed mortar additive technology has made great progress, wet-mixed mortar additive is different from concrete water-reducing agent to form a unique landscape, the product is mainly divided into liquid and powder two forms. Liquid additives are generally divided into a single component and two components, single component additives compared with the applicability of two components, flexibility is poor, because the two components can be adjusted according to the change of mortar raw materials, mixing station can be optimized after confirmation. Compared with the liquid admixture, the main problem is the metering and mixing uniformity of the mixing station. With the depletion and limitation of natural sand and stone resources in our country, no matter what kind of admixtures, their adaptability and compatibility are very important. Therefore, the adaptability of mortar admixtures should be applicable to the characteristics of raw materials and workers' construction habits in different places, and the production of mortar applied to the site can be approved by construction workers and project acceptance for more than one year (through different seasons).
3 Ends
Wet mixed mortar quality control is a big topic, not a simple article can tell the complete, this article mainly introduces the methods and experience of quality control based on the hot or prone to problems in the actual case, hoping to help the relevant technical personnel who really need this knowledge, but also look forward to experts and professionals to share more knowledge and experience of wet mixed mortar quality control.
Article source： Keyword：
Key words: wet mixed mortar quality fluctuation case analysis
1 Introduction
In 2016, the Central Committee of the Communist Party of China and The State Council issued Several Opinions on Further Strengthening the Management of Urban Planning and Construction, which made special instructions on improving the evaluation system of green energy-saving buildings and building materials and promoting green buildings and building materials. Wet mixed mortar is a green building material widely used in housing construction and municipal engineering, and its environmental protection and energy saving function is increasingly prominent, which is an important aspect of the green transformation and development of the construction industry. From January to June 2016, the country produced a total of 35.1291 million tons of ready-mixed mortar, an increase of 4.715 million tons last year, an increase of 15.5%. Among them, wet mixed mortar: During the same period, the national output of wet mixed mortar totaled 4,661,800 cubic meters, an increase of 1,483,100 cubic meters from last year's 3,178,700 cubic meters, an increase of 46.66%. Wet mixed mortar accounted for 21.23% of the total production of ready-mixed mortar in China. As the industry gradually recognizes the advantages of wet mixed mortar in environmental protection, its development trend is obvious. However, wet-mixed mortar continues to develop steadily, requiring more industry people to constantly ask questions and sum up experience.
2 Common problems in wet mixed mortar production
Wet mixed mortar is cement, fine aggregate, mineral admixtures, admixtures, additives and water, according to a certain proportion, in the mixing station, after the measurement, mixing, sent to the use of the site, and used within the specified time of the mix. The common quality problems of wet mixed mortar are mainly related to the quality fluctuation of raw materials, the rationality of mix ratio design, production control, technical personnel production and quality control and environment. Based on the practical cases of quality problems of wet mixed mortar for many years, this paper summarizes some common problems in production for reference and guidance of relevant practitioners.
2.1 Fluctuation of cement quality
From the perspective of the influence of raw materials, cement is a relatively small probability of problems, but there are still cement quality fluctuations in the actual mortar quality cases every year that affect the performance stability of wet mixed mortar. The fluctuation of cement quality usually affects the consistency loss of mortar, viscosity and other construction performance, which shows that the mortar dries out after a few hours on the site, the viscosity becomes worse, and a lot of water is needed to carry out construction, and even the mortar hardens for a few hours.
2.1.1 Case analysis
The mortar of a mixing station has been continuously complained at the site, the mortar is loose, the viscosity is not high, the wall cannot be hung, the sand sense is coarse, and the mortar left in the station is black in color, not bright, astringent, and hardened in advance.
Through the experiment, it is found that the mortar state and performance of different brands of cement are very different. The preliminary conclusion is that the clinker and admixture of the cement brand used in the current production are different from those used in the previous production, which affects the mortar state and performance. In the evening, the production mortar was changed to the previous brand cement, according to the original mix ratio, the next morning the site to check the mortar situation, the workers responded that the mortar was easy to use, the workability was good, and there were no site complaints during the day.
Therefore, the cement brand replacement of wet mixed mortar and the switch of different batches must be done to confirm the performance and status of mortar. If there is an anomaly, it must be adjusted in time to ensure that the performance and state of the mortar meet the requirements of the standards and actual site construction.
2.2 Fly ash quality fluctuation
Fly ash is the waste residue discharged from coal-fired power plants. During the combustion of pulverized coal suspended at high temperature, the clay minerals contained in pulverized coal melt and form liquid drops. The chemical composition of pulverized coal fly ash fluctuates widely in different discharge types, fineness of pulverized coal and combustion conditions. Then, after rapid cooling, it becomes a fine spherical particle with a particle size of 1-50 microns. First of all, due to the rough surface of the irregular porous glass body of coal and fly ash, there are many water storage cavities, and the water demand increases, which reduces the activity of fly ash. In addition, the unburned carbon in fly ash is harmful to its quality. When the fly ash with high carbon content is mixed into cement, the water demand often increases and the strength is greatly reduced. In addition, when the unburned carbon meets water, a water-phobic film can be formed on the surface of the particles, preventing the infiltration of water into the fly ash particles, thus affecting the interaction between the cement hydration product Ca(0H)2 and the active oxide, and reducing the activity of the fly ash.
The experimental analysis conclusion in the paper "Study on the Effect of fly ash Quality on the performance of plaster-mortar" also mentioned that (1) After 25% cement is replaced by grade Ⅲ raw ash and ground grade Ⅱ ash, the water consumption of mortar increases, the water retention rate decreases, the working ability decreases, the consistency loss increases, the shrinkage rate increases, and the compressive strength and bond strength are greatly lost, which not only reduces the construction efficiency, but also reduces the construction efficiency. It is also very easy to cause the hollow drum cracking in the later stage of plastering mortar, so it is recommended to use cautiously or not in production. If one of the two must be chosen, the first choice should be ground grade II ash. (2) The addition of grade I fly ash and grade II fly ash can improve the workability of mortar, increase the water retention rate of mortar, reduce the consistency loss and shrinkage rate of mortar, and the loss of compressive strength is small; The later strength of the mortar mixed with grade I fly ash can even exceed that of the mortar replaced before, which can improve the construction efficiency to a certain extent and reduce the risk of mortar hollow drum cracking, so it is recommended to be preferred in production.
The quality fluctuation of admixture fly ash is the key factor affecting the performance of wet mixed mortar. The selection of fly ash quality affects the increase of mortar water consumption, the decrease of water retention rate, the deterioration of workability and the increase of consistency loss. In fact, the mixing of fly ash quality control is still insufficient, often ignored in the production of mortar test between batches of confirmation, until the site problems to pay attention to it. Fly ash quality fluctuations lead to mortar quality complaints in the site is more common, mixing station need to do several groups of fly ash mortar with different content test to adjust the production mix ratio.
2.3 Sand gradation and fineness modulus change
Sand is used as the aggregate of the mortar and plays the main role of aggregate filling in the mortar. Natural sand with fineness modulus of 2.3-2.7 should be preferred for fine aggregates used in the production of wet mixed mortar. If the machine-made sand is selected, whether there is a defect in its particle grading is considered, and fine aggregates with different fineness modules are required to be used together to obtain the mortar with appropriate particle grading. The content of fine aggregate has a great influence on the volume stability of mortar, and the volume shrinkage of mortar with a large content of fine aggregate is relatively small, and the probability of plastic cracks in mortar is correspondingly reduced. Therefore, the impact of sand gradation and fineness modulus changes can be improved by optimizing or matching sand, or by appropriately optimizing the overall mix ratio of mortar to make up for the impact of its deficiency.
2.3.1 Case analysis
The gradation of mortar reaction sand in a mixing plant becomes worse and the fineness modulus becomes larger, and the mortar cannot be in a good state according to the original matching ratio. Through on-site adjustment and optimization of the mix ratio, the appropriate increase of water reducing agent can improve the coating property of mortar and the uniform distribution of slurry, and the reasonable fusion of slurry and aggregate in the mortar system can be improved, and the state of mortar can meet the standards and site requirements.
Of course, the mud content of the sand also has a great impact on the mortar. The mud content of sand is recommended to be controlled below 3%, but the mud content in some areas often exceeds 3%. Then, the mortar production process needs to pay careful attention to the change of mud content, if beyond the control of the original mix system, the mortar sent to the site may have problems, such as the mortar opening time is shortened, the mortar shrinkage cracking and so on. Therefore, the mud content is beyond the control range of the original mortar mix ratio system, and the mortar mix ratio must be readjusted and optimized through experiments.
2.4 Rational utilization of circulating water
The waste water produced by concrete mixing station contains cement slurry, admixtures, aggregates and other alkaline substances, direct discharge will seriously pollute the environment, and the transportation with clean water has caused a huge waste. For this reason, many mixing stations now recycle waste water, and some mixing stations begin to use circulating water to produce mortar. At present, the use of circulating water to produce wet mixed mortar needs to be cautious, if the proportion of wastewater utilization is not well mastered, the mortar is prone to abnormalities.
2.4.1 Case analysis
The mortar produced by a mixing station at 10 o 'clock at night has a very small consistency to the site, and the tank car cannot discharge the material. The situation is investigated at the station, and the mortar returned from the mortar tank car is checked. The mortar loss is indeed very serious and the mortar status is very serious. The mortar can recover the construction performance by adding water reducing agent to blend the returned mortar. Next, the production mix, equipment, materials are checked, and the trial is carried out at the same time, no abnormal mortar was found, the equipment scale is no problem, the mix is no problem, no abnormal link was found, and then the production is carried out according to the original steps, with the car to the site, the mortar is normal. This happened again the next night, and the mortar returned to normal after a few carloads of production. On the third night of production, the water source is replaced for production, and the occasional loss of mortar consistency on the site is completely resolved.
The main reason for the mortar problems in the station is that the concentration of waste water in the storage pool is too high, there is production of concrete, and there is carboxylic acid in the waste water, which has a negative effect on the mortar admixture and affects its normal function and effect. Therefore, the production of mortar water should pay attention to the proportion of waste water. Because most mixing plants produce concrete and mortar at the same time, the impurities contained in the recovered wastewater are complex, and the high concentration of wastewater during production is bound to affect the consistency loss and slump loss of mortar or concrete.
2.5 Stability and adaptability of admixtures
In recent years, wet-mixed mortar additive technology has made great progress, wet-mixed mortar additive is different from concrete water-reducing agent to form a unique landscape, the product is mainly divided into liquid and powder two forms. Liquid additives are generally divided into a single component and two components, single component additives compared with the applicability of two components, flexibility is poor, because the two components can be adjusted according to the change of mortar raw materials, mixing station can be optimized after confirmation. Compared with the liquid admixture, the main problem is the metering and mixing uniformity of the mixing station. With the depletion and limitation of natural sand and stone resources in our country, no matter what kind of admixtures, their adaptability and compatibility are very important. Therefore, the adaptability of mortar admixtures should be applicable to the characteristics of raw materials and workers' construction habits in different places, and the production of mortar applied to the site can be approved by construction workers and project acceptance for more than one year (through different seasons).
3 Ends
Wet mixed mortar quality control is a big topic, not a simple article can tell the complete, this article mainly introduces the methods and experience of quality control based on the hot or prone to problems in the actual case, hoping to help the relevant technical personnel who really need this knowledge, but also look forward to experts and professionals to share more knowledge and experience of wet mixed mortar quality control.
Article source： Keyword：
