Problems needing attention in the use of polycarboxylate superplasticizer


Release time:

2015-07-28

Author:

New Earth Group

Source:

Problems needing attention in the use of polycarboxylate superplasticizer

In the production process of polycarboxylate superplasticizer, it is necessary to fully understand the various influencing factors of the product performance of polycarboxylate superplasticizer, adjust the synthesis process parameters in time to stabilize the product quality, and strengthen the technical reserve through joint or independent research and development to meet the market demand, which is very important to ensure the stability of the product performance of polycarboxylate superplasticizer. After ensuring the product, what are the problems we need to pay attention to in the use of polycarboxylate superplasticizer? Let's understand together:
Read the product specification in detail, and combine the experimental results and concrete material preparation for specific projects. When the concrete mixed with admixture is tested, the raw materials used in the project shall be used. The testing items shall be determined according to the design and construction requirements. The testing conditions shall be the same as the construction conditions. When the raw materials or concrete performance requirements of the project change, the trial mixing test shall be carried out again.
Avoid contact between polycarboxylate superplasticizer and iron materials: the transportation and storage of polycarboxylate superplasticizer shall not use iron materials (except stainless steel), but should use plastic, glass and other materials. Contact with iron sometimes causes a change in the performance of the polycarboxylate-based water reducer.
It is strictly prohibited to mix other water reducing agents or other types of admixtures, which has two meanings. First, the compounding of polycarboxylic acid water reducing agent (such as lignosulfonate, air entraining, defoaming, retarding and other components) can only be carried out by admixture manufacturers or suppliers. The users of water reducing agent, that is, concrete preparers, only need to check, accept and put into storage its relevant performance, and shall not compound any other components in it, nor shall other components be mixed into it due to negligence. The use of pumps and metering equipment for pumping and metering other admixtures without cleaning is absolutely prohibited. Another meaning is that concrete mixing equipment, transport vehicles, pumping equipment is best fixed for concrete mixed with polycarboxylic acid series water reducing agent, when the common mixing equipment, transport vehicles and pumping equipment, these equipment must be thoroughly cleaned before it can be used as concrete mixed with other types of admixture, and vice versa.
Strict metering of water reducing agent and mixing water: when preparing concrete mixture mixed with polycarboxylate water reducing agent, the water reducing agent dosage and water consumption shall be measured strictly according to the optimal water reducing agent dosage and water consumption determined by the laboratory, and the water reducing agent dosage or water consumption shall not be increased at will, so as to avoid adverse phenomena such as segregation, bleeding, hardening, increase of air content of the mixed concrete, which will affect the normal pumping construction and pouring quality of concrete. The moisture contained in the raw material sand and stone aggregate must be accurately measured and deducted from the total water consumption to prevent adverse consequences caused by inaccurate detection of moisture contained in sand and stone aggregate.
Correctly face the adaptability of polycarboxylate superplasticizer and cement/admixture: the adaptability of admixture and cement/admixture has a long history. Over the years, the adaptability research work for naphthalene superplasticizer and its compound products has achieved good results: firstly, through the efforts of researchers, concrete preparers, admixture producers, cement and admixture producers, concrete constructors and supervisors have realized this problem together, which has changed the situation that admixture producers and suppliers have always assumed all responsibilities in the past. Secondly, on the incompatibility between admixture and cement/admixture, it is attributed to many influencing factors, and has carried out in-depth research on its influence law, and has explored a series of effective solutions to the specific incompatibility between admixtures and cement/admixtures.
According to GB 50119- 2003 "Technical Specification for Application of Concrete Admixtures", when the concrete mixed with pumping agent is transported from the ready-mixed concrete plant to the pouring site, the method of adding pumping agent can be adopted when the slump loss of concrete is too large due to long distance, traffic jam or waiting time for pouring, which is not suitable for pumping or pouring construction, A certain amount of pumping agent is mixed into the concrete transport mixer to run quickly until the mixing is uniform, and the slump is measured to meet the requirements for pumping and pouring. In principle, when the slump loss of concrete mixed with polycarboxylate water reducing agent is too large due to unpredictable reasons, the method of adding water reducing agent twice can also be used to restore the fluidity of concrete, so as not to cause waste of concrete mixture. However, because the performance of concrete mixture is quite sensitive to the dosage of polycarboxylate superplasticizer, so in actual construction, the number of polycarboxylate superplasticizer secondary addition or not, the number of secondary addition, etc., should be in accordance with expert opinions, and strict tests should be carried out to fully verify its feasibility.
Strictly control the vibration radius and vibration time: due to the addition of polycarboxylic acid series water reducing agent preparation of concrete slump is generally larger, coupled with the low viscosity of the mixture, so the concrete mixture after pouring vibration radius and vibration time should be determined through the test, or should follow the guidance of experts. If the vibrating radius is too small or the vibrating time is too long, it is easy to cause structural defects such as serious decrease of concrete air content and serious stratification of aggregate phase and slurry phase.
Strengthen the initial curing, prevent cracking: in any case, for any concrete mixture, the initial and later curing after pouring is very important. Polycarboxylic acid water reducing agent has little effect on the dry shrinkage performance of concrete, or the addition of polycarboxylic acid water reducing agent does not excessively increase the dry shrinkage of concrete, which by no means means that the concrete mixed with polycarboxylic acid water reducing agent can relax or even cancel the curing. Like concrete mixed with other admixtures, the surface of concrete mixed with polycarboxylic acid water reducing agent after pouring, vibrating and compacting, such as secondary plaster, film covering or spraying, is very effective in preventing plastic shrinkage cracks. The continuous 7d or 14d moisture maintenance is not only the need for the normal growth of concrete strength, but also to prevent its dry shrinkage cracks. In order to enhance the cracking resistance of the concrete mixed with polycarboxylic acid, it is also necessary to add a certain amount of fiber, and this concrete still needs good wet curing to ensure that the structure does not crack.
聚羧酸减水剂

Key words: