Particle-Matrix Proportioning of High Strength Lightweight Aggregate Concrete

Production of lightweight aggregate concretes (LWAC) requires specific knowledge and processes in order to achieve good workability of paste and concrete. A particularly demanding case is high strength lightweight aggregate concrete, i.e. having 28-day characteristic compressive strength in the range 60-80 N/mm² with oven dry density equal or less than 2000kg/m³. Coarse manufactured lightweight aggregates themselves often lack particles smallerthan 2 mm, which together with open aggregate porosity causes a certain loss of workabilityduring the first minutes after mixing. An efficient way of improving this is by particle-matrixproportioning. The desired concrete workability can be obtained by combining the filler modified paste with a suitable amount of coarse aggregate particles. In order to investigate this, several different LWAC mixes have been tested with the lightweight aggregate Stalite, an argillite slate from the US. We found that the particle-matrix proportioning approach can give desired workability of the LWAC mixes. This methodology is economical since no increase in cement and admixtures dosage is needed.