Research On Hydration Mechanism Of Superplasticizer On Different Tricalcium Silicate Polymorphs

The essence of cement hydration is the hydration of different minerals, cement clinker containing 50% or even up to 70% C3S minerals and 5-15% of C3A mineral. The calcining process of cement clinker will inevitably introduce Cu2+, Mg2+, Na+, K+ and other impurity ions, which will lead to the structural lattice constant change of the C3S, making the main mineral C3S of Portland cement exists in many crystal polymorphs, and early hydration process of C3A have a major impact on the work performance of cementitious materials. The introduction of polycarboxylate superplasticizer into cement, which play an important role in modern concrete technology and applications, changing the cement hydration reaction process and the application performance of concrete. Thus, it is of great significance that reveal the influence of polycarboxylate superplasticizer to different crystal C3S and C3A hydration.This article relies on the National Key Basic Research Program of China ("973 " Program) "Environment-friendly basic research of modern concrete" to carry out research work. By hydration heat, NMR, SEM, we have studied the impact of polycarboxylate superplasticizer and silica fume on the hydration heat release process, hydration products of microstructure and morphology of different crystal C3S, also studied the impact of polycarboxylate on C3A hydration intercalation reaction by XRD slow sweep.Three C3S polymorphs hydration exothermic characteristics are obviously different. MC3S, RC3S hydration heat release rate peak was significantly lower than TC3S, and the heat of hydration delays, the 7d total of hydration heat release of three C3S polymorphs as follow:TC3S, MC3S, RC3S. A great quantity of needle stick of C-S-H gel are visible in that three crystal C3S hydration products by microcosmic morphology, and hydration products of C-S-H gel of MC3S, RC3S spread in the more widespread and hydration products of C-S-H gel of RC3S presents coagulation needle-stick-like structure composed of clusters;Study on polymerization degrees of C-S-H gel indicated that polymerization degrees of hydration products of three C3S polymorphs hydrated for 7 days favored a descending order:TC3S, MC3S, RC3S; and when hydrated for 60 days it was MC3S, RC3S, TC3S. When hydrated for 60 days, the signal intensity of Q1, Q2 of C-S-H gel increased greatly in comparison with those hydrated for 7 days. When samples doped with vinyl-poly (ethylene glycol)-based polycarboxylate superplasticizer (PC) and silica fume, the variations of polymerization degrees of hydration products identified with that of pure samples; whereas, their polymerization degrees improved in varying degrees.The shorter of main chain length or the longer of branch chains length in methoxy polyethylene glycol-methacrylates-based polycarboxylate molecule, the stronger of the delay in TC3S hydration within 3 days. Hydration products of those samples doped with PC1, PC2, PC4 favored higher polymerization degrees when hydrated for 7 and 60 days in contrast to the pure TC3S. Testing results of NMR shows that the polymerization degrees of hydration products increase when PC1, PC4, PC2 were added sequentially. In the samples that mixed with silica fume and polycarboxylate superplasticizer, the addition of silica fume leaded to a minor difference of influences on TC3S hydration resulting from different molecule structure of polycarboxylate superplasticizer.Study on the intercalation of methoxy polyethylene glycol-methacrylates-based polycarboxylate superplasticizer into the LDH layered structure hydrated from C3A indicated that polycarboxylate superplasticizer with short branch chains (SCL=6.2nm) intercalated into the LDH layered structure successfully. While polycarboxylate superplasticizer with long branch chains (SCL=8.3nm) failed in intercalation.