有碱速凝剂对超高性能混凝土的性能影响研究

Influence of alkaline accelerators on the performance of ultra-high performance concrete

为在常温养护条件下制备出高早强的超高性能混凝土(Ultra-highperformance concrete,UHPC),系统研究不同组分、不同掺量的有碱速凝剂(低碱、高碱速凝剂分别命名为NA1,NA2)对UHPC力学性能的影响,利用扫描电子显微镜能谱(SEM/EDS)分析UHPC早期水化产物的微观形貌及元素组成,并就有碱速凝剂与UHPC的相互作用机理进行探讨。试验结果表明:UHPC强度发展规律受有碱速凝剂组分及掺量的影响明显,相比于NA2,NA1对UHPC的早期抗压、抗拉和抗折强度有显著的改善作用。NA1掺量在1%~3%时,掺量越大,早期强度越高,但后期强度损失越大。添加NA1能加快UHPC的水化反应,促进单硫型水化硫铝酸钙(AFm)的形成和钙矾石(AFt)向AFm转化,有效提高UHPC早期微观结构的密实性。NA2中的氟离子参与水化,所生成的CaF_(2)晶体对C-S-H凝胶产生吸附、插层作用,同时较高的碱含量导致UHPC硬化浆体微结构的劣化,因而不利于UHPC强度发展。研究证实了有碱速凝剂制备高早强UHPC的可行性,为提升UHPC早期性能提供新的方向。

To prepare high early strength ultra-high performance concrete(UHPC)under room temperature curing conditions,the effects of different components and dosages(low-alkali accelerator and high-alkali accelerator were named NA1 and NA2,respectively.)on the mechanical properties of UHPC were studied.The micro-morphology and elements of UHPC early hydration products were analyzed using scanning electron microscope with energy spectrum(SEM/EDS).The interaction mechanism between the alkaline accelerators and UHPC was discussed.The results show that the strength development of UHPC is obviously affected by the component and dosage of alkaline accelerators.Compared with NA2,NA1 has a significant enhancement in the early compressive,tensile and flexural strength of UHPC.When the NA1 dosage is in the range of 1%~3%,the larger the dosage,the higher the early strength,but the larger loss of later-age strength.The addition of NA1 accelerates the hydration reaction of UHPC,and promotes the formation of calcium monosulfoaluminate hydrate(AFm)and the conversion of ettringite(AFt)to AFm,which effectively improves the compactness of the early microstructure of UHPC.The fluoride ions in NA2 participate in hydration,and the resulting CaF_(2) crystals have adsorption and intercalation effects on the C-S-H gel.Meanwhile,the higher alkaline content leads to the deterioration of the microstructure of the UHPC pastes,which is not conducive to the strength development of UHPC.It confirms the feasibility of preparing high early strength UHPC by adding the alkaline accelerator.The results can provide a new direction for improving the early performance of UHPC.