Influence of Rapid Heat Treatment on the Shrinkage and Strength of High-Performance Concrete

Jan Stindt,Peter Mark,Patrick Forman

doi:10.3390/ma14154102

Abstract

Resource-efficient precast concrete elements can be produced using high-performance concrete (HPC). A heat treatment accelerates hardening and thus enables early stripping. To minimise damages to the concrete structure, treatment time and temperature are regulated. This leads to temperature treatment times of more than 24 h, what seems too long for quick serial production (flow production) of HPC. To overcome this shortcoming and to accelerate production speed, the heat treatment is started here immediately after concreting. This in turn influences the shrinkage behaviour and the concrete strength. Therefore, shrinkage is investigated on prisms made from HPC with and without steel fibres, as well as on short beams with reinforcement ratios of 1.8% and 3.1%. Furthermore, the flexural and compressive strengths of the prisms are measured directly after heating and later on after 28 d. The specimens are heat-treated between 1 and 24 h at 80 °C and a relative humidity of 60%. Specimens without heating serve for reference. The results show that the shrinkage strain is pronouncedly reduced with increasing temperature duration and rebar ratio. Moreover, the compressive and flexural strength decrease with decreasing temperature duration, whereby the loss of strength can be compensated by adding steel fibres.

Highlights

Constructions with precast concrete elements like trusses, walls, tunnel lining segments [1], or beams made of high-performance concrete (HPC) [2,3] with a compressive strength between 55 and 100 MPa have been found to be advantageous compared to conventional cast-in place members
The results indicate that the shrinkage behaviour of the bars can be approximated even
For T = 24 h it is reduced to 66.8% or 44.9% compared to the reference samples without heat treatment (0.383 mm/m without steel fibres and 0.364 mm/m with steel fibres for T = 0 h)

Summary

Introduction

Constructions with precast concrete elements like trusses, walls, tunnel lining segments [1], or beams (modules) made of high-performance concrete (HPC) [2,3] with a compressive strength between 55 and 100 MPa have been found to be advantageous compared to conventional cast-in place members. Elements are prefabricated independently of weather conditions and in a time-saving manner. Due to the high load-bearing capacity of HPC, filigree and slender elements arise. Their durability increases due to the dense pore structure of HPC [4]. The precast elements are assembled on-site via dry joints, bolted connections or socket joints, for example, so that construction times are shortened, and costs are reduced [5]. Since there are no tolerance compensating joints due to a direct force transmission, fast installation depends essentially on the shape stability of the concrete elements [6]

Methods

Results

Conclusion