Experimental Program

Materials and Mix Design

Nine concretes were prepared based on two concrete base mix designs as presented in Table 1. Seven steel fibre reinforced concretes (SFRC) and two conventional reinforced concretes (RC) were included.

Concretes type I were conceived to simulate a concrete for structural pre-casting purposes with a compressive strength higher than 40 MPa, and concretes type II were designed to reproduce general purpose concretes with a 10 or 20 mm maximum aggregate size and a compressive strength ranging from 25 to 35 MPa.

For type I concretes a cement CEM I 52.5R type and a polycarboxylate-based high-range water reducing admixture were used, whereas for type II concretes the cement was CEM I 42.5R SR or CEM II/BM 42.5R. In those cases the water reducer was a poly-functional plasticiser. The dosage of plasticiser was adjusted for each concrete to obtain a 100 ± 20 mm slump. For all concretes, sand and coarse aggregates were crushed limestone.

Reinforcements

Variables related to fibre dosages and conventional reinforcements were selected to cover a wide range of post-peak flexural response of the SFRC elements with

Table 1 Base mixture proportions and concrete properties

Table 2 Characteristics of fibres

Fig. 1 Rebar reinforced specimens

concretes showing flexural strain hardening behaviour, concretes that keep the load bearing capacity practically constant (flat post-peak region) and concretes with steep losses of residual strength after first crack (softening behaviour). In all cases of fibre reinforcement steel fibres were used. Some characteristics of the steel fibres used are given in Table 2.

Concrete specimens without fibres as reinforcement, both for characterisation and creep tests, were reinforced simulating a conventional RC by means of two steel rebars positioned in a longitudinal way as shown in Fig. 1.

Table 3 summarises for all batches designations the reinforcement characteristics like fibre dosages, fibre brand and dimensions of conventional reinforcement.

Table 3 Reinforcement characteristics for all series