Effect of expanded slate aggregate on fresh properties and shear behaviour of lightweight SCC beams

Lightweight normal concrete (NC) and self-consolidating concrete (SCC) mixtures were developed using lightweight expanded slate coarse aggregate. The developed mixtures incorporated natural sand, metakaolin (MK) and fly ash (FA), and had a density in the range 1817–1984 kg/m³. All the mixtures were developed with variable compressive strengths (20–61 MPa), lightweight expanded slate to fine aggregate (ES/F) ratios (0·7–2·0), water to binder (W/B) ratios (0·35 and 0·40) and variable total binder contents (500 kg/m³ and 600 kg/m³). Tests of the fresh properties of the developed lightweight SCC mixtures included flow/passing ability, viscosity and segregation resistance tests. The developed lightweight NC and SCC mixtures were also used to cast 12 identical beams without shear reinforcement to examine their shear strength and cracking behaviour in full-scale concrete structures. The results of the trial mixtures performed on a wide range of ES/F ratios showed that a maximum ES/F ratio of 1·5 could produce lightweight SCC mixtures with acceptable fresh properties and compressive strength, while a maximum ES/F ratio of 2 was able to produce NC mixtures. Although an increase in ES/F ratio decreased the density of the SCC mixtures, it decreased the 28 d compressive strength, reduced the mixture flow ability and passing ability, and increased the segregation risk. However, increasing the ES/F ratio increased the normalised shear loads and post diagonal cracking resistance of all the tested beams. This is because the tested expanded slate aggregate proved to be relatively strong as it did not entirely break along the diagonal crack surface, even in mixtures of 61 MPa strength.