Experimental Setup for Measuring Long-Term Behavior of Green Reinforced Concrete Beams

Abstract

The behavior of reinforced concrete under long-term loading is an important topic when designing concrete structures. Creep and shrinkage of concrete and long-term deflections of concrete structures, mainly reinforced concrete beams, have been studied for many decades but because of the long-term nature of these tests, existing experiments are relatively scarce. More importantly, there are significant challenges when carrying out these tests. These include achieving optimal beam design to ensure a realistic stress distribution with a developed cracked state, measuring deflections from self-weight, adequately measuring elastic deflections and strains, and instantaneously applying the imposed load. The problem is exacerbated with the advent of sustainable structural concretes containing recycled and waste materials—green concretes; they possess specific properties and experimental results for these concretes are even scarcer.

In this paper, an experimental setup, designed to test the structural behavior of reinforced concrete beams in a four-point bending test under long-term loading, is described. Six full-scale beams were produced from natural aggregate concrete, recycled aggregate concrete and high-volume fly ash concrete—two beams from each concrete type, one loaded after 7 and the other after 28 days. The load consisted of beam self-weight and imposed permanent load. The beam design procedure is explained, which enabled an adequate stress distribution and crack formation with a minimum imposed load. A method was developed to use geodetic equipment and measurements to determine the deflection from self-weight and a special support and loading structure were designed to enable instant imposed load application and the measurement of elastic deflections and strains. The complete test setup, equipment and procedure are explained and the advantages and deficiencies of this approach are discussed.