دانلود رایگان مقاله خصلت سیمان ترکیبی قبل از صنعتی و اثر دمای پیش پخت

Abstract

This study aimed to determine the physical-mechanical, mineralogical and microstructural properties of a pre-industrially manufactured hybrid cement (HYC) containing 5% alkaline activator and less than 30% clinker. The effect of the initial curing temperature (25 ± 1 or 85 °C for 20 h) on hydration kinetics and the development of compressive strength were also explored. The hydration products formed were characterised using XRD, SEM/EDX and 27Al and 29Si MAS-NMR. The findings showed that pre-industrial hybrid cement sets when hydrated with water and hardens to a 28-day mechanical strength of 35 MPa. The main reaction product formed was a mix of cementitious gels: C-(A)-S-H and C-A-S-H. Curing at 85 °C for 20 h, shows a behaviour similar to OPC, inhibited ettringite formation and generated more polymerised gels, enhancing 3-day but not 28- or 90-day mechanical strength.

4. Conclusions

This report on a pre-industrial hybrid cement with a low clinker content manufactured with an alkaline activator shows that the production of cement with a very low clinker factor and high mechanical strength is feasible. The material in question set and hardened at ambient temperature, giving rise to a binder with higher mechanical strength than required for general purpose cement (UG) under Colombian standard NTC 121, and for class 32.5 cement defined in European standard EN 196-1.Hybrid cement owes its good mechanical strength to the main hydration product, a mix of cementitious gels C-(A)-S-H þ C-A-S-H. These gels take up a larger percentage of aluminium and are more intensely polymerised than traditional C-S-H gel. In hybrid cement a high pre-curing temperature expedites hydration reactions in much the same way as in OPC and alkaline cements. Raising the temperature from 25 to 85
C accelerated the initial reaction in the cement studied, which exhibited 3-day compressive strength values of up to 30 MPa. Nonetheless, the subsequent development of mechanical strength was slower than when the cement was pre-cured at ambient temperature. Initial curing at 85
C for 20 h induced the formation of more polymerised gels (lower ratio) and inhibited ettringite formation (or favoured its swift decomposition), at least during the first 90 days, the maximum age of the materials analysed here. The possibility of delayed ettringite formation (DEF) at later ages in these thermally pre-cured hybrid cements cannot therefore be ruled out.