Performance And Mechanism Of New Crystal Nucleus Based Hardening Accelerator

Hardening accelerator is one of concrete admixture that often be used in the production of cement and concrete products, concrete engineerings need a quick and low temperature or negative temperature construction. There are problems such as workability reducing, strength retraction, the elastic modulus sluggish, alkali aggregate reaction, generic cream etc. in the using of traditional hardening accelerator. It’s a important issue that how to develop and apply new hardening accelerator with significant early strength effect and has no adverse effects on the performance of concrete, in the research and application of concrete hardening accelerator.This paper focus on the performance and mechanism of the new crystal nucleus based hardening accelerator Vivid300(CN). The influence of Vivid300(CN) to the liquidity, setting time, and volume stability of mortar was studied by the mortar liquidity experiment, the setting time, drying shrinkage test. The influence of Vivid300(CN) to the strength development of mortar and concrete was studied by mechanical testing of mortar and concrete. The influence of Vivid300(CN) to the cement hydration temperature development was studied by analysis of cement hydration temperature under confined conditions. By the test of chemical combined water, the influence of Vivid300(CN) to the hydration degree of cement was studied. Based on the Krstulovic-Dabic model, the effect of Vivid300(CN) on the cement hydration kinetics was discussed. The effect of Vivid300(CN) to the composition and morphology of cement hydration products was analyzed by using X-ray diffractometer and scanning electron microscope. Based on the above research, the mechanism of new crystal nucleus based hardening accelerator was analyzed.The experimental results showed that: The new type crystal nucleus based hardening accelerator Vivid300(CN) can’t cause the mortar’s fluidity decrease significantly. Vivid300(CN) can shorten the setting time of mortar with the increase of the dosage when used in combination with polycarboxylate superplasticizer. Be used with early-strength polycarboxylate superplasticizer, Vivid300(CN) don’t shorten the setting time of mortar when the dosage is less than 2.0%, and shorten the initial setting time and final setting time of mortar significantly when the dosage is 5.0%. The new crystal nucleus based hardening accelerator can make the temperature peak of hydration of cement in advance and increase, and accelerate the process of cement hydration; The new crystal nucleus based hardening accelerator can accelerate the formation of early hydration products of cement, and improve the hydration degree of cement; The new crystal nucleus based hardening accelerator does not make the cement hydration to produce new phase, and can promote the early hydration product C-S-H gel’s formation. The new crystal nucleus based hardening accelerator can significantly improve mortar’s and concrete’s super early strength within 1d; The new crystal nucleus based hardening accelerator does not cause the late strength of mortar decrease; In steam curing condition, the new crystal nucleus based hardening accelerator can effectively improve the demoulding strength of concrete, for example, the demoulding strength of the test cube mixed 5.0% new crystal nucleus based hardening accelerator, after 3h steam curing at 50℃, rised by 160% compared with the blank group.The mechanism analysis of new crystal nucleus based hardening accelerator show that: The new crystal nucleus based hardening accelerator’s main component A provides the fine crystal nucleus to the formation of early hydration product C-S-H gel, and reduce the crystal nucleation and growth resistance of C-S-H gel, and accelerate the early formation of C-S-H gel. A large amount of generated C-S-H gel cement ettringite calcium hydroxide and other hydration products together, and accelerator the formation of cement paste structure, and improve the compactness of cement stone. Thus the new crystal nucleus based hardening accelerator play a hardening accelerating effect. The research about the new crystal nucleus based hardening accelerator Vivid300(CN) in this paper will provide supports for the use and development of the concrete hardening accelerator base crystal nucleus.