The following problems must be noted in order to apply polycarboxylate admixture safely and efficiently.
Method I
Improve technology level, stabilize product quality, and strengthen technical reserves:
Only a few manufacturers are capable of independent research and development of polycarboxylate water reducer products in China, most manufacturers introduce technology from university scientific research institutions or research institutes, or directly introduce technology from other enterprises in production according to survey. It is difficult for manufacturers to adapt to various changes in raw materials and process due to own limited technology power, and insufficient in-depth understanding on the technology for producing polycarboxylate water reducer. Therefore, it is impossible to stabilize product quality.
Therefore, it is recommended that polycarboxylate water reducer manufacturers can actively cooperate with universities and research institutes, fully understand various factors affecting performance of polycarboxylate water reducer, and timely adjust and integrate process parameters to stabilize product quality. Technical reserves are strengthened for adapting to market demand through joint or independent research and development. Raw material standards of polycarboxylate water reducer should be launched as soon as possible. The price stability of polycarboxylate water reducer raw materials is very important to ensure performance stability of polycarboxylate water reducer products.
Method II
Believe in test results rather than product manual
Some fantastic products on water reducer manuals and even products with excellent test results are not suitable for some concrete projects. On the contrary, although the test products of some products are not very outstanding, they can just meet the requirement on concrete material preparation in some projects. In addition, the test results during project bid invitation can not represent the condition of actual implementation of the project due to changes in raw materials. It is clearly regulated in '2.1.4' of GB50119-2003 'Technical Specification for Concrete Admixture Application': raw materials for concrete blended with admixture, such as cement, sand, stone, additive and admixture shall comply with regulations in current national related standards. When concrete blended with admixture is prepared, raw materials for projects should be adopted, test items should be determined according to design and construction requirements. Test conditions are the same as construction conditions. Trial mixture test should be further implemented when the performance requirements of raw materials and concrete for the project are changed.
Method III
Avoid contact between polycarboxylate water reducer with iron materials
Special production equipment and production line should be adopted for composing and formulating polycarboxylate water reducer aiming at producers and suppliers of polycarboxylate water reducer. The production line should not be shared with other water reducers for composing and formulating polycarboxylate water reducer. In addition, polycarboxylate water reducer should not be transported and stored by tools made of iron materials (except stainless steel), but tools made of plastic, glass, and similar materials. The performance of polycarboxylate water reducer will be changed during contact with iron materials.
Method IV
Resolutely avoid mixing with admixture in other varieties
Mixing with other water reducers or admixture of other varieties should be forbidden for the following two reasons: firstly, polycarboxylate water reducer should be formulated by admixture manufacturers or suppliers only (such as lignin sulfonate, air-entraining, defoaming, retarding and other components), users of water reducer, namely preparers of concrete, should accept and warehouse the water reducer after related performances are tested, any other components should not be compounded inside, and other components should not be mixed due to carelessness. It is absolutely forbidden to use pumps and metering equipment for pumping and metering other admixtures without cleaning. Secondly, concrete mixing equipment, transport vehicles and pumping equipment should be solely used for concrete blended with polycarboxylate water reducer. When mixing equipment, transport vehicles and pumping equipment are shared, these equipment should be completely cleaned, and then the concrete blended with polycarboxylate water reducer can be used, and vice versa.
Method V
Strictly measure water reducer and water for mixing
Concrete mixture blended with polycarboxylate water reducer should be prepared in strict accordance with the best water reducer dosage and water dosage determined in the lab during measurement. Water reducer dosage or water dosage should not be randomly increased, thereby avoiding segregation, bleeding, hardening, gas content increase and other adverse phenomenon in the prepared concrete, thereby affecting normal pumping construction and casting quality of concrete.
Water contained in raw material sand and stone aggregates must be accurately measured, which should be deducted in total water dosage. Adverse effect due to inaccurate test of water contained in sand and stone aggregates should be avoided.
Method VI
Correctly handle adaptability problems between polycarboxylate water reducer and cement/additive
The adaptability of admixture and cement/additive has been discovered for long term. Excellent effect has been achieved from adaptability research aiming at naphthalene series high-efficiency water reducer and its formulated products over the years: firstly, the problem is jointly recognized by concrete preparers, admixture producer, cement and additive producers, concrete constructer, supervisor, etc. through vigorous propaganda by researchers. The previous situation of bearing all liabilities by admixture producers and suppliers is changed. Secondly, the inadaptability between the admixture and cement/additive is caused by many influence factors. The influence rule is deeply studied. In addition, a series of effective solutions have been developed aiming at concrete inadaptability phenomena of admixture and cement/additive.
Method VII
Accept expert guidance and implement strict test during secondary addition of polycarboxylate water reducer
When concrete blended with pumping agent is transported from ready-mixed concrete factory to the pouring site, it is not suitable to implement pumping and pouring construction possibly due to long distance, traffic jam, or too long time of waiting for pouring and too large concrete slump loss, and the method of adding pumping agent for the second time can be adopted, a certain amount of pumping agent is mixed into concrete transportation
mixer truck for fast turnaround until the concrete is mixed evenly, and the concrete can be pumped and poured after the slump is consistent with requirements according to measurement according to GB 50119- 2003 'Technical Specification for Concrete Admixture Application'. In principle, when too large slump loss is caused in concrete blended with polycarboxylate water reducer due to unpredictable reasons, method of adding water reducer for the second time also can be adopted, thereby restoring concrete liquidity and avoiding waste of concrete mixture. However, since concrete mixture performance is quite sensitive to the dosage of polycarboxylate water reducer, segregation, bleeding and even delamination can be easily caused once excessive water reducer is used. In addition, the influence of secondary addition of polycarboxylate water reducer on concrete performance is studied hardly. Secondary addition of polycarboxylate water reducer, secondary addition dosage, etc. should be based on expert suggestions, which should be strictly tested during actual construction, and the concrete can be poured after the feasibility thereof is fully validated.
Method VIII
Strictly control vibration radius and vibration time
Since the concrete prepared by mixing polycarboxylate water reducer has higher slump generally, in addition the mixture viscosity is lower, the vibration radius and vibration time should be determined by test after concrete mixture is poured, or expert guidance should be followed. Concrete gas content can be seriously reduced easily, aggregate phase and slurry phase are seriously delaminated, and other structure defects are produced due to too small vibration radius or too long vibration time.
Method IX
Strengthen initial curing and prevent cracking
Initial curing and subsequent curing are very important after pouring under any occasion for any concrete mixture.
Polycarboxylate water reducer has lower influence on dry shrinkage performance of concrete, or dry shrinkage of concrete is not excessively increased due to blending with polycarboxylate water reducer. It does not mean that maintenance of concrete blended with polycarboxylate water reducer can be loosened or even cancelled.
Surface secondary plastering, thin film coverage or spraying, etc. is very effective to prevent the plastic shrinkage cracking after concrete blended with polycarboxylate water reducer is poured and vibrated compactly, which is the same as concrete blended with other admixtures. Moisture maintenance for consecutive 7d or 14d is required for normally increasing concrete strength on one hand, and it also can prevent its dry shrinkage cracking.
It is very necessary to add certain amount of fiber at the same time in order to enhance crack resistance of concrete blended with polycarboxylate water reducer. In addition, the concrete still should undergo sound moisture maintenance, thereby ensuring no crack of the structure.
Method X
Construction and management units should work closely with concrete preparers and admixture suppliers
Various technical problems are inevitably encountered, technical arguments and even contradiction disputes due to project accidents should be met in the project. It is believed that all parties participating in the project have the final purpose of implementing the project smoothly, and ensuring project quality. Polycarboxylate water reducer is produced and applied in actual projects for short term. Accumulated project experience is quite limited. Difficulties in the aspect of application can be easily produced, and even project accidents can be caused. Construction unit or management unit should cooperate and deeply analyze with concrete preparers, polycarboxylate water reducer producers and suppliers as well as cement/additive producers and suppliers from the perspective of technology under the condition, and it is especially important to propose effective solutions.
