A study on mechanical and pressure-sensitive properties of cement mortar with nanophase materials
Introduction
Health monitoring of structures by embedded or attached sensors has been gaining increasing interest and is more effective to guarantee structural safety in service. However, smart concrete, which can sense its own strain and damage, is more attractive due to its strong mechanical properties and self-monitoring characteristics. Smart concrete with short carbon fiber has been systematically developed [1], [2]. The advantages of intrinsically smart concrete in contrast to smart sensing materials such as optical fibers, piezoelectric sensors, etc. are low cost, great durability, absence of mechanical property degradation due to the embedding of sensors, etc. [1].
In consideration of nanoparticles with many novel properties and significant improvement on some properties of materials mixed with nanoparticles such as nanophase ceramic, etc. [3], [4], cement mortars mixed with nano-SiO2 or nano-Fe2O3 were proposed and fabricated, and their mechanical properties and self-sensing of strain were experimentally studied in this paper. The results indicated that cement mortar with nano-Fe2O3 could sense its own compressive stress in the elastic and inelastic regimes because the volume electric resistance of cement mortar with nano-Fe2O3 could change with the applied loading. This property is valuable for structure health monitoring in real time. Furthermore, the compressive strength of cement mortar with nanoparticles was also simultaneously improved.
Section snippets
Materials and specimens
Cement mortar is composed of small grains of hydrated calcium silicate gels and large crystals of hydrated products, with nanosized individual pores and capillary pores (structural defects) distributed among them. There should be room for nanoparticles to improve the properties of plain cement mortar. Fe2O3 nanoparticles in the amounts of 3%, 5% and 10% by weight of binder (the sum of cement and nanoparticles) were used, and the same amount for SiO2 nanoparticles. Nano-SiO2 was obtained from
Compressive and flexural strengths
Table 3 shows the compressive strengths of all specimens. It can be seen that the compressive strengths of the specimens with mixtures A-2, A-3 and A-4 (cement mortar with nano-Fe2O3) at the 7th and 28th day were all higher than that of a plain cement mortar with the same w/b. As for the strength at the 28th day, the effectiveness of the nano-Fe2O3 in increasing strength increased in the order A-4<A-3<A-2 (with the decreases on the nano-Fe2O3 volume fraction). Furthermore, the strength
Conclusions
The compressive and flexural strengths of cement mortar with nano-SiO2 or nano-Fe2O3 were both higher than that of plain cement mortar with the same w/b, indicating that nanoparticles are valuable for reinforcing cement mortar.
Besides the enhancement on the strengths, the fractional change in resistance ΔR/R0 linearly decreases with increasing compressive loading and the change is more sharply with increasing the content of nano-Fe2O3, indicating that the cement mortar with nano-Fe2O3 is better
Acknowledgements
This study was financially supported by NSFC grant No. 50238040, and Ministry of Science and Technology grant No. 2002AA335010.
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