Effects of the shape, size, and surface roughness of glass coarse aggregate on the mechanical properties of two-stage concrete

Because two-stage concrete (TSC) is obtained by placing coarse aggregate in formwork and then filling the gaps with flowable grout, the properties of the coarse aggregate can notably affect the mechanical properties of TSC. In this study, uniaxial compressive and splitting tensile tests were conducted on TSC with eleven types of glass coarse aggregate of different shapes, sizes, and surface roughness for coarse aggregate. Two types of spherical glass aggregate with diameters of 17 and 30 mm, irregular shape of crushed glass plate classified into two size groups (20–30 mm and 10–20 mm) were used. Surfaces of spherical glass aggregates were two types; those were smooth and rough. The compressive strength of grout matrices used in specimens was 44.6 N/mm2 in the normal-strength mixture and 129.8 N/mm2 in the high-strength one. The relationship between the compressive and tensile strengths and the size of the coarse aggregate changed depending on the grout matrix strength and roughness of the coarse aggregate surface. The tensile strength for crushed glass aggregate were larger than those for spherical glass aggregate. Increasing roughness of the coarse aggregate surface led to an increase in the tensile and compressive strengths. The modulus of elasticity was affected by not only the solid content aggregate but also the shape and roughness. Moreover, the mechanical properties of TSC were compared with those of conventional concrete with the same coarse aggregate and same water-cement ratio as TSC. Observations from the test program indicate the design parameters that most strongly influence the strength and stiffness of TSC specimens. •Effects of shapes, sizes, and roughness of aggregate on TSC strength were investigated.•Effects of aggregate size changed depending on grout strength and its roughness.•Increasing roughness of the coarse aggregate surface led to an increase in the strength.•The modulus of elasticity was affected by the shape and roughness of aggregate.