Effect of water/cement ratio on micro-nanomechanical properties of the interface between cementitious matrix and steel microfibers in ultra-high performance cementitious composites

Vanessa Fernandes Cesari,Philippe Jean Paul Gleize,Milton Domingos Michel,Fernando Pelisser

doi:10.1590/s1983-41952021000400013

Abstract

abstract: Ultra-high performance concretes with steel microfibers have been studied in depth with the aim of producing more efficient and durable structures. The performance of these materials depends on the characteristics of the interface between microfibers and cementitious matrix. This research investigates the micro-nanomechanical properties of the interfacial transition zone between the steel microfibers and the matrix of ultra-high performance cementitious composite. The effect of the water/cement ratio and distance from the microfiber were analyzed. The results confirm the formation of high-density calcium-silicate-hydrate (HD C-S-H) matrix at higher concentrations than low-density calcium-silicate-hydrate (LD C-S-H) for w/c ratios of 0.2 and 0.3. The properties in cementitious matrix interface with steel microfibers were very similar to that measured for the cement paste, and no significant difference was observed regarding the distance to the microfibers in relation to the elastic modulus, hardness and chemical composition. Thus, the authors can conclude that the formation of a less resistant region does not occur at the interfacial transition zone cement paste/microfibers.

Highlights

Ultra-high performance concrete (UHPC) is frequently studied in order to develop more efficient materials for use in engineering projects
Considering that LD C-S-H particles have a characteristic elastic modulus below 25 GPa and HD CS-H above 25 GPa, the results show the formation of 96% of HD C-S-H and 4% of LD C-S-H when the w/c ratio was 0.2, and 63% of HD C-S-H and 37% of LD C-S-H when the w/c ratio was 0.3
This research evaluated the effect of the w/c ratio and the micro-nanomechanical behavior at the steel microfibercementitious matrix interface on the development of ultra-high performance cementitious composite

Summary

Introduction

Ultra-high performance concrete (UHPC) is frequently studied in order to develop more efficient materials for use in engineering projects. UHPC is produced with high binder consumption, a very low water/binder ratio, the absence of large aggregates and the use of steel microfibers [1]. This concrete presents high resistance to both compressive and flexural strength [2]. According to Scrivener et al [3], the presence of a solid element prevents the packaging of the particles next to it to be equal to the packaging and distribution of the same particles in the rest of the matrix. This leads to the occurrence of a more fragile zone (interfacial transition zone, ITZ) with different properties from the rest of the matrix

Results

Discussion

Conclusion