Ultra-High performance concrete (UHPC) with polypropylene (Pp) and steel Fibres: Investigation on the high temperature behaviour

Francesca Sciarretta,Stefano Fava,Marco Francini,Luca Ponticelli,Mauro Caciolai,Bruno Briseghella,Camillo Nuti

doi:10.1016/j.conbuildmat.2021.124608

Abstract

Ultra-high performance concretes (UHPC) are advanced cement-based materials characterised by superior mechanical properties with respect to normal and high-strength concretes; however, their dense and compact matrix can facilitate the onset of spalling at high temperatures. This problem is often coped up by adding polypropylene (PP) fibres to the mix design, alone or with other types of fibres; steel fibres enhance the material’s tensile capacity. The paper presents a series of tests on two UHPC types (150 and 180 N/mm2) with PP fibres (0.27% of volume) and variable content of steel fibres (0% to 1.92%), aimed at investigating the residual mechanical properties of the material after high temperature exposure. The experimental results are compared to available research on small UHPC specimens exposed to high temperatures, with dosages in PP fibres from 0.03% to 2%, and in steel fibres from 0 to 3%. The results of this research demonstrate that UHPCs need hybrid fibre reinforcement (PP + steel) to withstand high temperatures, and that the residual strength increases after 200 °C exposure, at all steel fibre dosages; this is in line with literature. Available research also shows that strength loss is possible in hot conditions, as found in the present research, while PP fibres alone do not always prevent the occurrence of spalling in small UHPC samples.

Highlights

In the last 25 years, ultra-high-performance concrete (UHPC) has been gaining attention in the field of construction industry and research, due to its very high mechanical strength, high energy absorption ca pacity in tension and durability [1,2]
Ac cording to the study by Stengel and Schiessl [4], the mean quantities of the different components in UHPC mixes are outlined in Table 1, where the volume fraction is the ratio of quantity to density
Observing the original values, the 28-days compressive strength of CLS-A shows no relevant variation with the fibre content

Summary

Introduction

In the last 25 years, ultra-high-performance concrete (UHPC) has been gaining attention in the field of construction industry and research, due to its very high mechanical strength, high energy absorption ca pacity in tension and durability [1,2]. To define this class of advanced cement-based materials, the minimum strength of 120 N/mm, i. E. the upper limit of high-strength concrete (HSC), is generally accepted [3]. The superior properties of UHPC are due to its peculiar mix design, which includes only fine aggregate (maximum grain diameter < 1 mm), and low water to cement ratio (generally not higher than 0,25). Other prominent applica tions are high-rise building columns, precast bridge girders and foot bridges [8–11]

Results

Discussion

Conclusion